How to take front cover of bryant (non-programmable) thermostat

Hi, I have this (Builders Non-Programmable Thermostat) from bryant and i try to replace with programmable one. Some how i have trouble to take out the current one front cover so i can replace with the new one. Does any one has this kind of thermostat before. I would be appreciated for your help.
Here is the link for the model i have:
http://thermostatusa.com/BryantResidential.asp
The last one on the page.
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