The only way to "clean up" a credit score is to pay off bills and wait.

The biggest problem in doing this is many people simply can not pay off their bills. Many are out of work and have no income, or their income is so low, there is no way short of winning the lottery.
That said, I have a low tolerance for people who have built up large credit card and other bills. I, for example, haven't owed anything on a credit card since 1991. I keep a strict budget. It's not just if I don't have the money I don't buy it, my rule of thumb is how much have I saved this month according to my budget - Left over (after savings) is what I have to spend.
One thing that hit our family hard was setting a very rigid budget for eating out. 1) The family drank water. They did not like that. Now... that's about all they will drink. 2) They learned that the family had $75.00 a week to eat. Use it how you wish; one meal; three $25.00 meals; Mon-Wed; Wed; Friday; Sunday; etc.
I didn't literally use the envelope systems; but used the notion of "here's what you have; when its gone its gone. It made a large difference for our family.
