How to run word press theme on localhost in Ubuntu OS?

Here is two method for downloaded theme.

  1. Then login as admin and navigate Dashboard >> Appearance >> Themes.
    Then click on Add new button then click on Upload theme button and browse download theme zip file like theme.zip. and click on install button.
    After installing theme click on activate theme button.

    Note : Your wordpress folder have read/write permission.

  2. Paste your downloaded theme into themes directory located at your_wordpress_folder/wp-content/ directory.
    Then login as admin and navigate Dashboard >> Appearance >> Themes and active your downloaded theme.

    View How To Install A Theme On Localhost tutorial for more guidance.