You can just delete the profile altogether if you can't remember what you changed, but I guess the other way would be to make a note when you change something. I don't do this as I rely on my memory, but it doesn't always work. Remember you can't really break anything with it, just change one thing at a time, and if it doesn't work then just change it back and start again. A bit like setting up a car. The temptation is to change everything at once to some recommended setup, but so much about graphics quality is subjective and also dependant on your hardware configuration that it is worth taking the time to do it slowly and properly. The compromise that you make to get your ideal settings will almost always different for different people, even if they have the same hardware, take advice, change one thing at a time, and keep what works for you and discard the the rest.