Steps:
1. Downloaded cm-10.1-20130705-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (82fe5f63e00081b7d5066efbc581dfa8).
2. Reboot into CWM Recovery.
3. Created backup.
4. Flashed cm-10.1-20130705-NIGHTLY-i9100.zip
5. wipe cache partition.
6. advanced > Wipe Dalvik Cache.
7. Reboot.