You can download the latest version of Joda-Time here. Once the "joda-time.jar" is in your classpath, you will be able to use Joda-Time.
The release notes for upgraders can be found here:
Unless you have a specific reason to do otherwise, it is advisable to use the
binary download. If you want to build Joda-Time from source you will need
Apache Ant.
Simply call ant jar
to compile and create a jar file.