I used to be a cosmetician and had a lot of people inquire about how to get rid of them. Here's 3 things that could help:
1) a skin lightening gel or cream (spot treatment wands are best) what it does essentially is bleach the skin.
2) Use a MicroDermabrasion or peel, the glycolic % encourages exfoliation of the skin.
3) To prevent any future spots, really important to use high SPF especially on the spots you already have.
Any more questions, let me know, I'd be more than happy to help.