The most common way of installing a theme is through FTP. If your theme files (theme.html, style.css, images) are already inside a folder, upload that folder inside the Theme Directory (..themes/). If they are not in a folder, create a new folder inside the Theme Directory and upload the theme files to that new folder. Remember that the name of the folder becomes the name of the theme from within the XOOPS Admin Control Panel.

Once you've uploaded the theme and the theme files, go back to Administration Menu -> System Administration -> Preferences -> General Settings and choose your theme from the “Selectable themes” dropdown box. Save changes.

An extra step is to delete all cached files from within the templates_c/ folder using an FTP client. It is safe to delete all files in that folder, but it is prudent to leave the index.html file in there. This extra step ensures that you are looking at your new theme instead of cached files of the old theme.

If you made changes to your theme after it is installed, go to the Administration Menu -> System Administration -> Preferences -> General Settings and set “Update module template .html files from themes/your theme/templates directory?” to YES. This will allow XOOPS to look for new or changed theme files in the Theme Directory.

Go to your home page and check out your new theme. If everything is okay, go back to Administration Menu -> System Administration -> Preferences -> General Settings and set “Update module template .html files from themes/your theme/templates directory?” to NO.