An Easy Way and a Hard Way
If you are lucky, you might be able to get errors fixed the easy way. If one of your creditors is the source of an error, you should try to get them to stop reporting erroneous information. A phone call may be all it takes. You can bring a mistake to their attention, and ask that they correct it. Once their records are correct, that information will flow through to the credit-reporting companies.
If you are not so lucky, you will have to go through the unpleasant process of disputing errors in your credit report. Credit-reporting companies say that they do not create records on you — all they do is repeat what others report on you. If you cannot figure out who is reporting something derogatory about you (if it is not one of your accounts that simply has an error), then you have to sort it out with the credit-reporting company.