Download the plugin and extract it into the plugins directory.
Go to the plugins directory and run :
bundle install --without development test RAILS_ENV=production
If you need to migrate the database then run the following command :
rake redmine:plugins:migrate RAILS_ENV=production
Now restart redmine :
You should now be able to see the plugin list in Administration -> Plugins and configure the newly installed plugin
Uninstalling the plugins :
rake redmine:plugins:migrate NAME=plugin_name VERSION=0 RAILS_ENV=production
Remove the plugins directory and restart redmine.