Get Rid of the Old Window

• All caulk that's holding the exterior trim in place must be sliced away at this point. The interior trim has to come off, so utilize a flat bar to do the job. Free the window by using an electric saw to cut in between the wood buck and frame. Cut between the window frame and the wood buck to free the window.
  
  

The Opening

• The most important part of this job is making certain that the window is installed square. Use a level to confirm that the sill is flat and the buck square. If the opening is big enough to contain the replacement window, build an inner buck using 1-by-4 lumber. Should the buck be slightly out of square, use a shim to fill any small gaps. A shim is a thin wedge of wood, metal or stone used for driving into crevices. However, you'll need to construct another buck if it's out of square by a great deal.
  
  

The Replacement is Ready

• Now install the new window into the opening. If you've used shims, they should now provide a very close fit for the window. To lock the window into place, screw through the frame of the new window and into the buck. Inspect the window to make certain that the screws are able to adjust the window. This is done to confirm that the window is square. All trim, both exterior and interior, should now be replaced.