This ID was a customized username you chose when registering a new account prior to Microsoft's acquisition of Skype. If you made your Skype account in the early days, your unique username may still be available.
Regardless, an existing username or a new randomly generated name cannot be altered at this time. You may, however, modify your Skype display name to make it simpler for friends or employers to locate you for instructions.
Your Skype ID may be accessed on your Skype profile, in the mobile apps for iPhone and Android, and on the desktop software. The procedures are nearly the same in both cases.
