Server Window Has Former Coworker's User Name

Every time I log onto my server at work, the pop up window where I input my name and password has my former coworker's name autofilled and I have to delete his user name and put in my own. This has always been my computer so I'm not sure why his name keeps appearing. Is there anyway I can permanently remove his user name so it doesn't appear? I've attached a screenshot. I've tried a few google searches but I don't know how to search for this particular situation. Thanks for any help.