My garage door is opening on its own - mostly in the middle of the night. When it does this, the door won't shut and is unresponsive to either the button on the wall of the garage and the remote trasnmitters. I have to shut it using the emergency release. I opened up the garage door unit to search for a place where I can switch the codes, but cannot find any. It is a Craftsman 1/2 hp model# 139.53615SR. Anyone have any idea how I change the code for this unit? Thanks.