Measure the window opening
Remove the old window if needed
Clean the opening
Check that the opening is level and square
Apply flashing or waterproofing as needed
Place the new window into the opening
Shim the window until it is level, plumb, and square
Fasten the window according to the manufacturer’s instructions
Insulate gaps around the frame
Seal the exterior with caulk
Install interior trim if needed
Test the window to make sure it opens and closes properly