1. Download the following files:
- Gingerbread ROM
- Gapps
- GPRS version 12 (optional)
2. Mount your android phone into PC and put all downloaded files above into sdcard.
3. Reboot into recovery
4. Wipe all data (cache, dalvik, factory reset)
5. Flash from zip file using this sequence:
- 1st = Gingerbread ROM
- 2nd = Gapps
- 3rd = GPRS version 12
6. Reboot the phone and wait until the screen dim.
7. Done
Reference: XDA Developer Forum