First, enter the contributor name correctly (Accounts>Contacts).  Then, go to Transactions>Contributions>Monetary Contributions and use the “browse” button to find the contribution you need to change.  On the contribution window delete the name currently listed in the “contributor name” field, use the F11 key to get a list of your contacts and choose the correct name from the list.  Click OK to save your changes.  Last, you will need to file an amended C-3 to reflect the name change.