Perforce is the best change management software that I have used. It used to be free for a simple two user system, but now that seems to have been expanded to 20 users..! Set up a P4D server somewhere, and then install the P4 client on your local machine(s). Then, you simply book in all of your existing documents, and simply check-out the document that you wish to change. Make changes with whatever tool to what to use, and then when you are finished you check it back in (as well as any newly created files) along with a short comment (AKA a change description) to remind you later what that change was.
The thing that makes Perforce better than other change management systems is that you can make atomic changes. That is to say, you can change a number of different documents at the same time, and check them all in at the same time, under the same revision number and the same comment- you don't have to check each document in one at a time (repeating the change description each time), which can be particularly annoying if the are all related to the same change.
The reminder comment does not have to be too verbose as Perforce comes with a (web based) diff tool that can compare any change against any other (not just the previous one) and show you all of the pertinent changes across all of the files in a colourful GUI.
Command line tools and platform specific GUI applications are also provided.
Easily the most complete solution by far. And no, I do not work for, or own shares in Perforce (although, hmmm, maybe I should...)