There are so many causes for hyper pigmentation and uneven skin tone.
There is systemic pigmentation which is damage at the cellular level. This is very difficult to treat on a superficial level and even the most aggressive medical treatments will not be able to eliminate the problem entirely.
Then there is surface pigmentation which is generally more successfully treated. However a lot can be done to brighten and lighten the skin and protect it from further damage.
Using a Sun Protection (SPF) of 30 and above is recommended to protect the skin.