how to replace Thermostat.. and what are the cause of Low Air conditioning cooling?.

What do you mean by low cooling, if its low output of cool air, that could be a lot of things like a dirty filter.

Hello Friends.....

The first step is to remove the cover from your old thermostat. It might just pop off, or there might be screws holding it in place. Don't remove the entire unit yet, just the front plate or cover.

Inside your old thermostat, there will be a number of wires, all fastened to points inside the unit and disappearing back into the wall. Each wire will be labelled (either on the wire itself, or at the connection point) with a letter. With labels that come with your new thermostat, or pieces of masking tape, clearly mark each wire

Thanks

@marlon: Thanks for that advice. Does it apply to all thermostat? Or is there a particular thermostat that works that thing that you posted?