In general, we assume that you are managing installation of ictime via the Universal PlugIn Manager (UPM) of JIRA.
Installation
In JIRA, go to
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.
Update
In JIRA, go to
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. The new version will be automatically downloaded and installed.