Search and find the user record
Click on the username to edit
Check when the course was added that they would like to swap
Check the date of purchase, and the usage. If it was purchased within the last week and there is no or little usage, then it is okay to swap the course, by selecting the course to swap out, use the <- arrow to move it to the left and use the -> right arrow to move the desired course to the right.
After a change, press the update user button at the bottom of the page
If there is a lot of usage over a number of weeks, reply to the customer that it is not possible to swap after it has been used for some time.