If you're gonna break code just for the sake of refactoring, I would seriously consider leaving i alone, specially, if you are going to affect other people in your team who may be depending on that code.
If your team is OK with this refactoring, and investing your time in doing this (which may be a time-saver in the future, if it means the code is more readable/maintainable), use Visual Studio (or whatever IDE you are using) to help you refactor the code.
However, if a big change like this is not a risk your team/boss is willing to take, I would suggest a somewhat unorthodox, half-way approach. Instead of doing all your refactoring in a single sweep, why not refactor sections of code (more specifically, functions) that need to be touched during normal maintenance? Over time, this slow refactoring will bring the code up to a cleaner state, at which point you can finish the refactoring process with a final sweep.