I use Gimp, which like a free version of Photoshop. There is online help, including YouTube videos. It takes a bit of practice but I find that I don't need to know everything, just enough to allow me to do what I want to do.
I've used it for restoring old black and white family photos (including replacing half of someone's head!) and it has made them much clearer. I've also restored lots of old colour pictures that had gone yellow.
How did you vote and why today
What colour car do you have or did you used to drive?
So, find a program first, then look for a tutorial. Good luck!