You just need to open your project in a newer version of Mendix and it will ask if you want to upgrade your project to use that version.

There are sometimes breaking changes so it is worth reading the release notes and upgrading any marketplace modules you may be using to the latest versions at the same time.

Hope this helps.

 

You can download a new Mendix version from the appstore. 
Open the Mx version, select a project from the teamserver and open it. Mendix will then convert it to the new Mx version.