the easiest way is to disconnect the battery again... you have to leave it disconnected for a short period of time (try a minute or so) to let the radio reset. You can also pull the memory fuse (located in the under-hood fuse box usually), its normally a 7.5 amp fuse... also, leave it out for a minute or so.

once its powered back up, put the proper code in and you should be all set.

good luck.