First, it is important to note that we want to record the way the credits appeared on screen. If your name is spelled wrong on the screen, we still want to record that fact.
Let's say, though, that all the credits listed for you in the database are wrong. Easy enough: Look up the misspelled name, scroll to the bottom of the page and click on the Edit Page button, and choose Name Correction / Add Correction. Click on Continue, and fill in the forms that follow. There's a very important check box on this page marked "update existing credits with 'as' attribute"-- if the listing we have matches what appears on screen, you should check this box.
Example time: You are John Doe, and that's how you want your credits to read. However, you were once credited as Jack Doe, and we have a listing for you under that name. You should look up the Jack Doe credit and check that box when you correct it. By contrast, if you actually were credited as John Doe on that project, you should not check the box.
Note that if you are combining credits that were listed under two different variants of your name, you will get a warning that you are combining credits for two names. That's OK; that's exactly what you want to be doing. However, you should double check that all the credits under both names really are yours.