The location of the window makes it a perfect place for water to gather and cause rot in the wood. If you are handy with tools, then replace is an easy fix; however, if you don’t feel comfortable working on windows, try calling a professional. You can find one at a local hardware store or an internet search. Rotted wood must be removed for the window to fit properly in its opening again. For this, you will need Hammer, Palm Sander, Tape Measure, Screwdriver, Power Saw, Screws (long enough to support wood paneling), Wood Glue and Drill.