As long as you have an active Gliffy license and Admin rights, you can update the Plugin any time from the Universal Plugin Manager (UPM)
1. Open the Administration menu and select Add-ons.
2. Log in with your JIRA Admin credentials.
3. In the sidebar, select Manage Add-ons.
4. Scroll down and locate Gliffy Diagrams for JIRA. If an update is available, you will see an Update button. Click to update the plugin to the latest version.