Hello,
First of all, make sure you are signing in using the admin user.
Type sysdm.cpl in the search on the taskbar and hit enter, go to Advanced tab, click on the "Settings" button at the User Profile section. Then delete the old user profile.
Next, hold down Windows + R keys, type in netplwiz and press enter. When launched, find the old employee username and delete it. (Note, this step will only work if the user is a local user or a Microsoft account, if your computer is domain joined, then this step is not necessary).