Replacing bottom screen on a nintendo DS
The bottom screen is not difficult but it does take some care. As noted in another post, the bottom screen is 3 pieces. The actual screen, the touch screen on top, and then a clear plastic cover.
There is a ton of videos and manuals out here that can get you started.
Two things though!! Wear examination gloves when working with the touchscreen. Any fingerprints on the screen and it will not function correctly. I have had a limited amount of success cleaning the screen after my pudgy fingers hit it.
Also, It can be difficult to get all of the screens lined up correctly. Make darn sure you look at the spacing all the way around BEFORE you pull the stack apart. If you do not get it all lined up correctly the case will not fit! (Even then it may take of couple of tries to get it right)
Good luck with it.