I am sure you have seen all of the advertisements around the Internet for credit repair agencies. You see them on the web, TV, and billboards and hear them on the radio. Some say that you only need to make one call and they will take care of the rest. I have a tip for you, it is a scam. The only credit repair agency that will work for you is you.
The two keys to credit repair are simple. 1. Cut off the problem now. 2. Wait seven years.
If there is something bad on your credit report, get rid of it. I have seen credit reports that show a credit card that is paid fine today but had several 180 day past due payments a year ago. Pay off the balance and close the card. From the time you close the card, it will take seven years for the record to drop from your report. If the card is still open, it will say indefinitely.
Pay off anything that looks bad and close it. As they get older, your score will rise. Eventually it will go up as if the bad information was never there. This goes for all loans, credit cards, collections, bankruptcies, and judgments.
So, to fix your credit deal with the problems and close the accounts. It might be tough for a couple months, but do everything in your power to pay off any balance on an account that you screwed up at some point. It is no one's fault that it was not paid except for your own.
In the rare event that the credit company made an error (it does happen), you need to get in touch with that bank and with the credit agency. An error will be corrected by the bank and taken off the report, but you have to prove that it is an error. It is a hassle to fix, but you can and should do that ASAP.
Do you have any questions about credit repair? I am happy to answer them in the comments.