retrofit reinstallation

Hi, I'm new to this site but have done some construction work. My biggest project was the design and construction of my 8x10 foot storage shed. I am a woman and I only weigh 120 pounds, but I built the whole thing myself and it's still standing and in great shape 13 years later. :) Now I am...

Anyone know if it is very difficult to reinstall a retrofit window? Lowe's installed a window and it is leaking on the inside when it rains. It was a while ago they installed it so it isn't under warranty anymore. It doesn't rain a whole lot in San Diego so we didn't notice it quick enough...