How do I replace the exterior wall without damaging the siding?
I really think you have a situation that is going to be a bit more than a novice carpenter should tackle. The normal procedure to replace wall framing involves placing a pretty hefty beam under the ceiling joists and jacking the entire section of joists at once so the weight is off the stud walls. The studs and plates can then be removed. Other considerations will be electrical, windows etc. It is going to be impossible to properly replace the entire wall frame without also removing the exterior sheathing and siding.

What you are faced with is a MAJOR repair. You will need all the right tools, calculate the proper wall height, plumb the walls, interlock the corner plates together, support the roof load, and try to do this fairly quickly as the house is going to be wide open for a while during this process.

This is a good example of when you should hire a pro and see if he/she will allow you to assist. You will learn a lot and have the security of knowing the roof isn't going to fall down on you during the process. Consider the costs as tuition in you carpentry education.