Go to Tools> (Tools) Folder Options (Folder Options).
On the View tab (View), select Show hidden files and folders and then click Apply and OK.
Double-click Local Disk (Local Disk) (C:).
Double-click the Users folder (Users).
Double-click the folder with your user name Windows.
Double-click the folder AppData.
Double-click the folder Roaming.
Double-click the Skype.
Delete the folder with the Skype UserName you want to remove from the login screen.
Double-click the Macintosh HD icon on your desktop.
Open the folder ~/Library/Application Support/Skype/ (Note: the sign ~ means your home directory. You will find your root folder by opening Finder and by selecting Open> Home in the menu bar or by pressing the *Command (Apple), Shift and H
Delete the folder containing the username you want to remove from the the login screen.