Xoops come with several pre-install themes that you can use by default. However there are a lot more themes developed for Xoops, which you can use on your site. You can find some free Xoops themes here:
http://xoops.org/modules/extgallery/
Once you have found the theme which you wish to use on your Xoops website, download its archive on your local computer and extract it. You will have a new folder with the same name as the theme you have downloaded. Upload that archive in the “themes” folder of your Xoops website. The “themes” folder is located in your Xoops root directory. You can upload the theme using FTP. You can find our FTP video tutorials here:
https://tmdhosting.com/tutorials/video/ftp.html
To activate the theme, go to your site’s admin panel. Click on “Templates”:
Now you can select a new theme:
Click the “Submit” button when you have selected theme.
You have successfully installed and activated your Xoops theme.