Steps:
1. Downloaded cm-10.1-20130317-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (10e752c7539e82a379cc361afc2712a7).
2. Reboot into CWM Recovery.
3. Created backup.
4. Flashed cm-10.1-20130317-NIGHTLY-i9100.zip
5. wipe cache partition.