I haven't transferred a registration before so I want to know if I have to get new plates when I do it?
You can transfer the vehicle plates you have along with the registration to another vehicle you own
what do I do with the plates if I don't transfer the registration?
If you do not transfer the registration, you will need to surrender the vehicle plates to the DMV.  You might be eligible to receive a refund if you surrender the plates before the registration expires.