If you are rooted, you can get any rooted ROM, download it and flash it in recovery.
If you are not rooted and you want to go back to stock, you can download the Official HTC image here: Stock Images | PvilleComp's
The RUU's are .exe programs that you can run with the phone connected to your PC. Load HTC Sync first so you have the correct drivers. You can find that here: Tools | PvilleComp's
The PB31IMG files are flashable from HBOOT on the phone itself. There are How to's here: How To… | PvilleComp's