Obviously we had a little problem last night with your blog themes.
I have fixed that now and added in a few more themes so you can personalise your blogs.
To change themes just go to “Appearance” >> Themes and select your preferred theme.
Some themes work better once you add “widgets” to them.  You can find them under ”Appearance” >>Widgets
A word of warning – while the “Buddypress Home Theme” will work, it is not ideal as blog theme.