How do I treat/prevent acne all over my body?

I’ve had a lot of pimples on my back since like 5th grade and now, it’s starting to spread to my chest. I also have a lot on my face…what do I do?
I’ve also got lots of these shadows of pimples where there were pimples but it’s gone…not completely though. Like I said, there’s like these brown spots…it makes me look soooo ugly…T_T