How to Install WordPress Themes and/or New Version on Byethost?

Does anyone know how to install wordpress themes on byethost? I usually use fantastico and there’s an option to choose wordpress, but only version 2.8.5. Is there any way to install newer version of wordpress there?
If I choose to install version 2.8.5, there will be only two themes that I could choose to use. Is there any way to install other themes?