When you log into Skype the different usernames are displayed in the dropdown menu of the login window.
If you want to remove your username or names of persons who logged in to the Skype application installed on your PC, follow these steps (for Windows 7):
Close all the running instances of Skype.
Click the Start menu, then type Run in the search box and press Enter
In the "Run" tab, enter the following command:
Several folders will be displayed and some will be named after the different Skype usernames, which have been used via the application installed on your PC. Select the folder with the username that you want to remove from the login window and delete it.