Check out the CRA's website and look for the link to disputing credit information. You can usually start the process there. Write a letter to the CRA correcting the inaccuracies. Include vital information like your name, address, social security number, etc. and request that a correction be made. You might even copy your report, highlight the mistakes and include it in the envelope. Send it with a return receipt requested documenting that they have received the information. Put all your copies of letters sent in a folder.
If there is a vendor or creditor supplying the data, write a letter and indicate you are disputing their information. Include copies you sent to the CRA.
If you haven't heard from the CRA in thirty days (the time allotted in which they must legally respond to you) give them a call using the customer support number provided on the credit report. Don't forget to jot down the particulars of the conversation so you know what will be done.
The CRA, when responding to your dispute, will include a current copy of your credit report if they have made changes.