Ramin,
Our latest version is MyEclipse 2015 CI 6, which is based on Eclipse Luna. I’m afraid you cannot directly upgrade to MyEclipse 2015 from MyEclipse 2013.
You can upgrade to MyEclipse 2015 CI only by downloading and installing the Bundled Installer (offline installer) / Online Installer from here. For more information on MyEclipse 2015 CI, please check this delivery log. You can install MyEclipse 2015 alongside your existing MyEclipse 2013 installation and give it a try.
If you are holding a license for MyEclipse, then the same license can be used for all the versions of MyEclipse, as our licenses are time based not version based.
Hope this helps and let us know if you see any issues with MyEclipse.