How do you switch shipping carriers and print on Ebay?

I've noticed that when you ship a package with FedEx and go to print the label it allows you to choose which carrier you want to ship with, but when you have an item be shipped with UPS and click the print shipping label button it takes you to a screen where you can link a ups account. I realized after sale that I selected my item to be sent with the wrong carrier (UPS) and messaged my buyer and he said it was okay if I shipped with FedEx instead. For a variety of reasons it makes more sense for me to ship through FedEx. How can I print my label so that I can still get Ebay's discount?