1. Downloaded cm-10.2-20130831-NIGHTLY-i9100.zip and copied to internal SD. Verified MD5 checksum (57c8450efbd3cf145dfb751c595fbd9c).
2. Downloaded gapps-jb-20130813-signed.zip and copied to internal SD. Verified MD5 checksum (1f51b5cc6370c1f45dc951109b6ce6ed).
3. Reboot into CWM Recovery.
4. Created backup.
5. Flashed cm-10.2-20130831-NIGHTLY-i9100.zip
6. Flashed gapps-jb-20130813-signed.zip
7. wipe cache partition.
8. advanced > Wipe Dalvik Cache.
9. Reboot.