You have to hard reset the M1/M2 and delete the Slingplayer app you want to use to set up the M1/M2 and re-download it. Then do set up all over again. I was unable to find this info in the FAQ's.
I believe the Slingbox FAQ has info on how to hard reset a M1/M2. Basically press a paperclip in the reset hole on the back until the red light behind the network icon flashes twice. Then wait for the red light on the right side to start flashing. Then bring up the Slingplayer app and set up the M1/M2.