How do I change reading in C degreeas to fahrenheit?

I expect that it depends on the specific model of thermostat, but I found link to the owner's manual for one model here:

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=3&cad=rja&ved=0CDYQFjAC&url=http%3A%2F%2Fwww.ntsupply.com%2Ffiles%2Fproduc ts%2FRS_9515.pdf&ei=D3SFUMSAL6nD0AGX7ID4CQ&usg=AFQjCNHIpWm0-mgUOwgxB_Q8VqMB0IMm3w&sig2=TtxtjdzevlkkNG-hmB6oPg

And it indicates that there is a F/C switch on the circuit board (which you access by removing the cover, and then: