In the states I've lived in, the state DMV office sends a renewal notice (online or by mail) before the expiration date in order to renew.
Alternatively, I now live in a state where I have an account online with the state govt for issues just like this one - my car, voting, etc. so I can go in and renew that way.
If I were you, i would go onto your state's website and search under vehicle registration and likely you will find directions there.
When we give up the need to be special, life becomes special.