Post [Q] Need help with updating

Hello all, I'm new to this forum and I could really use some help with my phone. I have a rooted AT&T Samsung galaxy S3 running on 4.1.1 stock with cwm. I would like to update to the latest stock OS which is 4.3 but I'm not sure how to do it right. I would prefer to keep all my data but I don't mind losing root. how should I go about updating my device safely?