Welcome to the BBForums!

The themes really don't change that much in this series, except that you can find lots of free and pay themes around our Media Section here.

Downgrade the OS: How do I downgrade the OS on my BlackBerry? - BlackBerryFAQ

Find the OS you want by following the initial post in this thread that says "Previous OS thread Here" and clicking through those until you find one you like.

Good luck.