You follow the same procedures for upgrading Jenkins Enterprise as you do for Jenkins. Detailed steps on upgrading Jenkins from a previous version can be found at the Jenkins wiki.

If you are already running community Jenkins, and Jenkins Enterprise is based on the same version (or newer), you can upgrade your installation by simply starting to run the Jenkins Enterprise WAR with the same $JENKINS_HOME. If you were running a newer version of community Jenkins, and do not wish to downgrade, use the Jenkins Enterprise metaplugin to add the Jenkins Enterprise plugins to your existing installation.

Any bundled plugins (those which were packaged in the Jenkins Enterprise WAR) will also be updated to the new bundled versions, assuming you did not explicitly update them originally. If you did update them previously, they will be shown as pinned in the Plugin Manager interface (details); these will not get updated automatically, even if the newly bundled version is newer than what you have installed, so you should consider updating them after the core upgrade. Click Check now in the Advanced tab since the update center definition varies according to the Jenkins core version. Check the plugin release notes (normally hyperlinked from the plugin name in the Updates tab) to see if you want to accept updates; in some cases a plugin update will be mandatory for a core upgrade, i.e. the older version of the plugin was found to be incompatible with the new core.