I'm curious about treatments that can treat back pigmentation.

In preparation for the coming summer, I'm writing this because I have a concern that I really want to address during this time when I can cover my body with clothes.

I want to get my hands on it because the acne scars I had in the past are now brown and blotchy, and my overall skin tone on my back is uneven.
I tried applying whitening products at home, but I didn't see much effect because my back is hard to reach and the skin layer is thick.

I want to get my back clean through a treatment during the winter when my skin is less exposed. What treatment would be most effective for my case?

I'm wondering if it would be better to remove the old dead skin cells and pigments together, or if it would be better to destroy the deep pigments themselves.
It would be easier to decide if you could tell me the approximate recommended number of treatments, the level of pain, and the duration of the effects for each procedure. I would like to get it done this winter.