Changing themes in e107 is quite easy. You should log in as admin and go to Theme Manager. Once there, you will have a choice of several predefined themes which you can use for your e107 application. When you choose a theme, you should click on Set As Site Theme to change the theme for your site. Some themes also have a Set As Admin Theme button, which, as the name suggests, will change the theme of your admin area:

13

You can easily install more themes by uploading the zip file with the theme in the www/e107_themes folder. Then you should extract the archive using the File Manager in your cPanel. Once the theme archive is extracted, you can set the theme as a default one for the admin area or for the whole site.

IMPORTANT!
You have to rename one file in the directory where your e107 is installed. The file is called filetypes_.php and is located in the e107_admin folder, rename it to filetype.php in order for the file to work. Otherwise you will not be able to upload any files through e107. You can rename this file with your favorite FTP manager or via cPanel > File Manager.