Photo restoration is one of the most complex tasks (or, more accurately, combination of tasks) that you can do with image-editing software. None of the more basic programs can do the job well, so you're really forced to use something like Photoshop (expensive) or Gimp (free) if you want to achieve decent results.
Gimp has a very steep learning curve so I'd normally avoid recommending it to a novice but, for the reasons I've given above, it's what I think you actually need for the task ahead of you:
https://www.gimp.org/
Fortunately though, you'll only need a fairly small subset of all the commands available in Gimp so, with a bit of help from Youtube, you should be able to get to grips with it fairly quickly. This guy has produced an excellent series of 7 easy-to-follow videos, which cover everything you'll need to know:
https://www.youtube.com/playlist?list=PL8IiFmgWlzv_6vcj3IaijCys9iH8tC2FO