How to Update an old theme for the latest wordpress version

WordPress is exceptionally backwards compatible, so it is typical even for older themes to just work for a long time.

However for solid results you would want to perform several meaningful actions:

  1. Straight up code review, if your experience and time allows. Just read through all of the code, gauge if it makes sense.

  2. Running through everything with WP_DEBUG enabled. Straight errors will come up, but also any formally deprecated functions/features will emit warnings with suggestions to update.

  3. Run through Theme Check plugin and see what comes up. You don’t necessarily want to bother with all of that for custom theme, but it’s a good to see what’s up.

  4. If you customize theme for private use — make a proper fork of it, changing name and details. Otherwise you risk invalid update from the repo destroying your changes. However do keep proper attribution to original author for copyright/licensing reasons.

Related Posts:

  1. Is having multiple theme customizers for different pages possible?
  2. How to export/import theme customizer settings?
  3. reason of splitting theme files to multiple files
  4. How to get the registered sidebar’s name by its id?
  5. Set the transport of the Customizer ‘header_image’ core setting to ‘postMessage’
  6. One button to change all settings in theme customizer?
  7. The best way to customize “nav-menu-template.php” to add if the ‘link_before’ is “checkbox”
  8. Design view breaking on Pages
  9. Use different javascript files for each page on website
  10. How to get custom image size for image uploaded in Customizer
  11. Passing array in add_option()
  12. Widgets not showing in my custom theme
  13. How do themes render caption texts in extended markup (e.g. “wp-caption” paragraphs)
  14. Changing the template hierarchy
  15. Can’t load WP function into external function
  16. Set WordPress Default Template
  17. Customizer: Output default value in Customizer CSS
  18. WordPress does not load page.php, return 404.php
  19. adding custom user input fields in WordPress admin dashboard gives error The link you followed has expired. Please try again
  20. Customizer: active_callback and sanitize_callback incompatibility?
  21. Compare the old get_theme_mod($name) to the new get_theme_mod($name) return value
  22. How do I link a button I created in theme customizer to a function?
  23. Is the “_s” on this `sprintf(__(‘Page %s’, ‘_s’), max($paged, $page))` just refer to a text domain?
  24. What does this mean in wordpress? Easy question
  25. Why am I getting a different filename? And how does WordPress load singular.php for both Page & Post? (Fresh WordPress installation)
  26. Reason to add a name of the theme like (‘menu-1’ => __( ‘Primary’, ‘twentynineteen’ ),) in PHP?
  27. Separation of presentation and code – WordPress
  28. WordPress Customizer Default Image
  29. Why in my theme I can’t see all the statics content under the posts?
  30. get_template_directory adding FTP root folders in urls
  31. How to add the sidebar to all the pages except the home page? [closed]
  32. Header not properly displaying on archive.php
  33. Save Custom CSS file in the upload folder dynamically?
  34. Warning: printf(): Too few arguments in helpers.php file
  35. home.php show blog posts as grid view
  36. get_comments_number() returns 0
  37. How to correctly load a different version of main menu based on the user language in WordPress? Is it a good solution?
  38. Why in this WordPress theme I can’t see the Main Menu?
  39. How can I assign separate stylesheets to different pages?
  40. How to make sure relative URL works when site is not on root domain?
  41. Commas in Tag Cloud
  42. WordPress redirects page query parameter in URL
  43. Dynamically switch file in get_template_directory_uri() | Function [closed]
  44. Uncaught TypeError: extract(): Argument #1 ($array) must be of type array, null given
  45. Not able to remove caption shortcode from the content
  46. When I click for the redirect link it is showing the content of index.php instead of single_assignment_page.php
  47. Unable to retrieve get_author_posts_url
  48. Display post date also if the date it’s the same for each post
  49. WordPress child theme, creating a custom php template page
  50. Menu to the right of screen on desktop using Bootstrap 4
  51. How to add Open/Close Toggle button into Twenty Fifteen theme for hiding left sidebar?
  52. Use Custiomizer to setup meta theme color tag
  53. Rotating Header Images
  54. Create a custom theme-specific page, invisible in the admin-panel?
  55. WP Knowledge Base Theme bug – Subcategories and Articles, Need to change WP_Query
  56. Image not displayed
  57. Predefine Magazine Style Layouts
  58. How to store the_post_thumbnail() value in a variable
  59. Need help with Deprecated: Non-static error when update PHP 7.4 -> 8.1 with Dyad 2 theme
  60. Font Awesome Icons as squares [closed]
  61. Gulp dev environment set up for WordPress theme development
  62. What is considered good practice for registering menu locations?
  63. The theme doesn’t load css and JS files doesn’t load in functions.php
  64. Upgraded php & wordpress but theme broke
  65. Remove update nags for non-admins [duplicate]
  66. Error Warning: Declaration of description_walker::start_el after PHP upgrade [duplicate]
  67. How to determine if WP_DEBUG is enabled? [duplicate]
  68. Get author full name
  69. Check php version before theme activation
  70. Is it possible to get a theme customizer setting from wp.customize using jquery?
  71. Activate different theme for temporary preview
  72. How to use copy() function and paste file in /wp-content/themes directory
  73. Twitter feed is showing blank in WP site [closed]
  74. How can I add a class to a single menu item?
  75. How do I hardcode a WordPress shortcode into my theme?
  76. Show different Customizer Settings on Page-Tamplates
  77. I think emoji are killing my WordPress site… How can I debug?
  78. Am I not understanding plugins?
  79. Custom Logo URL | Help me print the URL of the custom logo I inserted into my theme
  80. Why is this Ajax not working?
  81. Displaying theme options in css
  82. max_input_vars: how many am I using?
  83. How to load a template-part based on a url wildcard?
  84. Multiple WordPress Menus that will only display all pages
  85. Custom theme: Alternatives to long list of ‘include’ in functions.php
  86. How to show part of the_content?
  87. Hide categories that are not used in the post type
  88. Reconfiguring WordPress site
  89. Menu jumping when calling it via PHP
  90. Showing latest post without 301 redirect
  91. How to organize functions.php content
  92. excep tonly one css, don’t load any css
  93. Conditional Banners
  94. loop to return tags in woocommerce in alphabetical order?
  95. How to properly escape in ternary operators – Wp Coding Standards?
  96. need to edit php file of child theme to remove an element
  97. how to register a second page-template
  98. Gallery requires a featured image but does not show it in posts/pages
  99. require used as a function to load theme dependencies?
  100. Woocommerce Select Option Popup [closed]