Best left to a gunsmith.
If you go to You-Tube and type in disassemble of Smith and Wesson model 915;there should be a video of the steps needed to take down your smith and Wesson semi-auto 9mm.
You can get a manual for free at S&W's website
Does not exist.
No, no, no. Do not attempt to do this.
You can request a owner's manual for free at the SMITH AND WESSON web site.
Can't be answered without knowing what model.
100-450 or so
value depends on overall condition