1. Downloaded cm-10.1-20130404-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (49c500cfa46e80122f4365147ebde767).
2. Reboot into CWM Recovery.
3. Created backup.
4. Flashed cm-10.1-20130404-NIGHTLY-i9100.zip
5. wipe cache partition.
6. advanced > Wipe Dalvik Cache.
7. Reboot.
7. Reboot.