If you've installed Maven on a Mac OSX or Unix machine according to the details in Section 2.3.1, “Installing Maven on Mac OSX” and Section 2.3.3, “Installing Maven on Linux”, it should be easy to upgrade to newer versions of Maven when they become available. Simply install the newer version of Maven (/usr/local/maven-2.future) next to the existing version of Maven (/usr/local/maven-2.2.1). Then switch the symbolic link /usr/local/maven from /usr/local/maven-2.2.1 to /usr/local/maven-2.future. Since, you've already set your M2_HOME variable to point to /usr/local/maven, you won't need to change any environment variables.

If you have installed Maven on a Windows machine, simply unpack Maven to c:\Program Files\maven-2.future and update your M2_HOME variable.