I have a White-Rodgers thermostat #156-5259 and have lost the manual. What do I need to do to get a manual?

Go to the White-Rodger web site: redirect

There you can enter your model number, download a pdf, get replacement and trouble shooting info, other product info et. al.. Easy to navigate and really helpful web site. They also have video links that can show you how to replace your unit. A set back thermostat could save you some $$.