One of the good thing about a rutorrent seedbox is it has much more options from most of the Torrent clients put there.
By default your seedbox comes with the oblivion Theme
To change the Theme you have to click on the settings and on initial screen itself the theme option will show up:
You can click on the drop down and select the theme you like and click ok.
For Reference you can see below How rutorrent seedbox looks with different themes.
3. Acid Theme rutorrent
4. Agent46 Rutorrent Seedbox Theme
5.Blue There rutorrent Seedbox
6. Dark Theme rutorrent Seedbox
7. Excel Theme rutorrent Seedbox