The following upgrade steps are needed if you want to upgrade your project from Mod4j 1.2.0 to Mod4j 1.2.1 .
If you want to upgrade from earlier released versions, you'll need to follow the required upgrade steps as described in the subsequent Upgrade Notes for each release. For an overview of of the releases and Upgrade Notes, see the Mod4j Releases page
Before you install a new Mod4j Eclipse plug-in into Eclipse make sure you un-install older versions of the plug-in.
Here you can find download and install instructions, that will guide you to install Mod4j, by making use of the Mod4j updatesite.