Steps:
1. Downloaded cm-10.1-20130307-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (dd7b9058bfd0bd6dddd74d5632509147).
2. Downloaded gapps-jb-20130301-signed.zip and copied to internal SD. Verified MD5 checksum (b7e53e96e1c8b1a1c4865bf29418c8e0).
2. Downloaded gapps-jb-20130301-signed.zip and copied to internal SD. Verified MD5 checksum (b7e53e96e1c8b1a1c4865bf29418c8e0).
3. Reboot into CWM Recovery.
4. Created backup.
5. Flashed cm-10.1-20130307-NIGHTLY-i9100.zip
6. Flashed gapps-jb-20130301-signed.zip
6. Flashed gapps-jb-20130301-signed.zip
7. wipe cache partition.