How difficult is it to change the size of a window? I have the opportunity to purchase a new Pella bay window for my kitchen at an excellent price. The existing opening is 35" high by 72"wide. The new window would be 50" high by 74" wide, and weighs over 200 lbs. The wall is easily accessible from the outside. I'm not contemplating attempting the installation myself, mind you, but I'd like to have some idea of level of difficulty before I look for someone to do the work.