I'm guessing you didn't Nandroid backup beforehand? Then it would be an easy, one-step process...
Otherwise, backup your (user, not system) apps using something like Titanium Backup. Download the 2.3 ROM you want to flash, and put it on the root of the SD card. Reboot to recovery, then prceed to factory reset, wipe cache, and wipe Dalvik cache. Then flash the ROM you have on your SD card. Reboot, restore your apps from backup, and you're back to Gingerbread.