1. This is assuming you did our How To Root the HTC Tattoo procedure.
2. Make sure you have HTC Sync installed (http://member.america.htc.com/download/Driver//HTC%20Tattoo/HTC%20Sync%202.0.18/HTCSync.exe) and it can see your phone.
1. You should have a goldcard made from our How To Root the Tattoo procedure. Put it into the phone.
2. Plug the phone into the computer via USB, select HTC Sync and click Done.
3. Download whichever RUU for your device from here and save it to your computer.
4. Now with your phone plugged in and the goldcard in the phone, double click the RUU file you just downloaded.
5. Wait for it to finish flashing your phone. All done! Back to stock!