If you have admin access to your WP site you can login remotely via any web browser and use built in Updates function.
To login to your site visit http://yoursite.url/wpadmin (replace yoursite.url with your web address.
From your Dashboard you will see the Updates option which will check for updates of legitimate Plugins.
If you are updating a plugin you have written you can use the Plugin Editor function, also provided by WordPress and found within your Dashboard under the Plugins menu item. Again, any web browser should allow you to do this.
Another alternative would be to use an FTP Client, assuming your server allows FTP access. Via FTP you can upload an entire plugin thereby replacing the existing plugin files.
FTP
Note: When using FTP you must pay attention to any database changes the update might make. Using the supplied “Updates” function from your Dashboard would be a safer option and you are unlikely to break your site.
SSH
Your server may also offer an SSH option allowing you to connect to your server (if it is a Linux style server) and perform updates using other tools such as wget
I hope this helps you and doesn’t get down voted if I’ve misunderstood your question.