1. Downloaded cm-10.1-20130112-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (0074e0751ce136d2fcc2d1c4be6a9e2b).
2. Reboot into CWM Recovery.
3. Created backup.
4. Flashed cm-10.1-20130112-NIGHTLY-i9100.zip
5. wipe cache partition.