Several ways to do it and depends on what you want. If your already rooted you will need to un-root and go back to the stock
Sprint Froyo ROM
1. Confirm you have
gingerbread EI22.
2. Download
ACS recovery 1.0.0.5.tar.md5 file and this
file as well (you can use
CWM purple version as well if you don’t want the acs Recovery.)
3. Put the su-3.0-efgh-signed zip file onto your sdcard and turn off the phone.
4. Boot into Download mode by holding the 1 key on the keyboard and the power key
5. Open odin and connect the phone to the computer, one of the ID:com boxes will light up to confirm it is connected.
6. Odin
Mkasik's EI22 Keyboard fix Kernel put the file in the PDA area of Odin and make sure everything is uncheck except Auto-Reboot.
7. Once you have completed the above steps, place your device back into download mode again.
8. Odin the ACSrecovery.tar.md5 or the CWM purple version file using the same exact above method. If done correctly your phone should reboot directly into ACS recovery mode or CWM purple version. Once in recovery flash the su-3.0-efgh-signed zip file then reboot the phone.
Very easy my man, Samsung made it a little harder to have the custom recovery stick and this is why you must flash a custom Kernel as well. If you don't want this set up since it is as close to stock as you will get with Root and a Custom recovery you can always flash to a ROM already using Gingerbread and follow the Chef's directions.