I work in the office at the Fire Department. We have locked the system (a technician did it for us) so no one else can come and change it frequently like they had in the past. As winter approaches, we'd like to take it off cooling and put it on heat. I can't remember how to unlock it, make the change and relock it. I know we had to push 2 or 3 buttons at the same time, but just can't remember and I didn't write it down. Can you please help ?? thank you, Kathy Boyden