They are accessible via the Settings menu. On some views, you have to go down until you reach it; in others, you have to go up. The Settings option has a wrench icon next to it. Once you reach the Settings option, push OK.
Go to Appearance. You should see an option for Choose Theme which is pretty self-explanatory. I prefer the Metro Theme myself. MJT has another theme in progress but I don't know if it'll ever see the light of day.
Also, check out Appearance Options under Appearance. And from the Settings menu, also check out Menu Strip, Recycle Bin & Other Options.
Let us know how it goes. I'm glad to see new folks finding an appreciation for RTVHD.