Hi Mary -
From the title page here, click on the blue "Edit Page" button:

The "Edit Page" button will redirect you the the online Update form. You will need to select to "Correct/Delete" from the Cast drop-down menu and then click on the "Continue" button on the bottom:

You will then need to select "Correct" from the Action field next to the credit you want to update, and click on the "Check These Updates" button.

You will then need to replace the existing character name with the correct name, select the 'provide an explanation to assist in processing this change' box and click on the "Check These Updates" button.

The background will be green, you will need to enter your Explanation for why you are changing the data and click on the "Submit These Updates" button.