How To Get Rid Of Bumps And Dark Spots Caused By Shaving?

I have dark spots caused by shaving, I used a razor, as well as razor bumps. How do I get rid of them? I also have these on my head as I shave my head too. I get skin irritation on both head and chin after I have shaved and have to scratch a lot at times. The dark spots are on both my head and my chin. I m 50 yrs old and I m 1.65m.