Hi i live in California & have my car plates from here but i plan to move to Atlanta Georgia, do i need to change my plates & registration?

Hell yes you do. You're moving to another state, remember?

Your plates, driver's licence and auto insurance all have to be issued in the state in which you live. That's the law in all the states and provinces in fact, and you have between 15 and 90 days to get it done. (It varies between jurisdictions, and I didn't feel like looking up Georgia's laws)

This is important stuff, so don't ignore it. Whether the deadline is 90 days or 90 minutes, once you pass that deadline you're sunk.

Yes you do, and within a short period of time after establishing residence in GA.

Yes, of course you have to change your title, registration, insurance and your drivers license.

duh