To ensure that Skype provides their users with the “best communication experience possible,”older versions of the client (6.13 and below on Windows, 6.14 and below on Mac) are going to be retired over the next few months.
If you’re still using an old version, you can update to the newest version of Skype for free by following these steps:
- Visit the Skype for Computers download page.
- Download the latest version by clicking on “Get Skype for Windows desktop” or “Get Skype for Mac.” (depending on your operating system)
- Follow the setup instructions to complete the installation process.
- Sign in to Skype.
Source: Skype Blog