So I bought a used H21-100 off ebay and it works fine but the channel lineup is still set for the original owners area which is NY and I live in NC. How to I change this?

Usually you need to through the Sat Setup where it -- may be "Repeat Sat Setup" menu.

You could also do a "reset everything" and start from scratch.

If that doesn't work, go online and send a rehit to the box:
https://www.directv.com/DTVAPP/mydirectv/mysystem/mySystemResendAuthorization.jsp?_requestid=6032

Did Directv ever sell H21's outright or is this a leased model someone shouldn't have sold?

I guess it doesn't matter if Directv activated it for you.

You can't change the programming to your current city without activating the box through DirecTV and giving an account number. The box will show the guide for the "service address" associated with that account number. There is nothing you can do in setup for the receiver that will change that.