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Administration -> Plugins -> Install plugins
Either search for "ictime" and follow the instructions or upload the ictime .jar file if you have downloaded this file at another place.
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Administration -> Plugins ->Manage my plugins
If you are using a more or less current version of the JIRA UPM, you will see a list of all plugins with available update. If there is a new version available, you can click on the respective "Update" button for ictime (or you could chose to update all plugins). The new version will be automatically downloaded and installed.