Just re-run Guided setup to enter you new zip code.
After that is done, you will have to go through the tedious process of editing the channel list to select only the real channels that are available in your area - depending on where you are, that could be either a very short or long and painful process.
Once you have the channel list correct, you need to review your One-Passes to update any specific channels. Actually, I am not sure this last step is necessary; because, I have no idea if Guided Setup will wipe out your existing 1P list. But if they are not removed, most of them will probably be wrong unless you have them set them up to record from all channels.