I'm going to guess this is one of those QB quirks like not being able to switch a Bank entry if you accidentally put something in as a Deposit. You have to delete it to put it back in as a Payment.
So at this point, I'd pick the Class Name that has the fewer entries and change them all to the other name (even if it's the wrong Name). Once you're moved them all, try to Delete the name with no transactions. There is a chance you may need to log out and then back in for QBs to recognize there are no associated transactions.
Once you've got everything associated to one Name, edit it to what you want.
NOTE: One way to get all the items you're trying to change the name FROM is to create a Report for that Class Name. As you edit each one to the other name they should drop from your Report. So you'll have an idea of how many are left to go or a way to pick up the process again if you need to stop.
