Hi and welcome! You basically just have to disassemble the top and replace all of the interior parts that have deteriorated. There are numerous threads in this forum showing how people have done this.
Start by covering your floor and counter tops with cardboard. Remove cushions and curtains/blinds. Take measured drawings of curtain hardware. The reason the walls get water damaged is because the windows aren't taken out and resealed with butyl tape and Lexell caulk on the outside. Ask me how i know!! Look for back posts as many have had to do rebuilds. Use bracing on the inside with Towlites to hold the structure. Consider using metal where the cable cuts into the wood. This is a good time to replace the seal between the layers. Check the condition of the cables. We are here to answer any questions you may have. I used quite a few tools from Harbor freight.