There is a method to adjust them but I don’t remember how. You can find it on YouTube. I wonder why the top doesn’t slide out all the way. If it is cable driven, then the cables need adjusting, if it is track driven, then something might be restricting the upper portion from following the bottom driven track. See if something is binding up the top. Otherwise, do your research for a manufacturer’s directions for adjusting. You could also call the manufacturer for instructions.