You can uninstall the Matukio component just as any other Joomla component. Just navigate to Extensions -> Extension Manager -> Manage -> search for Matukio (component), select it and click uninstall. The uninstall process will remove all installed plugins and modules as well.
Normally the Matukio tables that hold the categories, events, bookings etc. are not deleted. If you want to remove them as well during the uninstall process, then go to the Matukio dashboard -> options -> and on the advanced settings tab set the "complete uninstall" option to yes. Now when you perform an uninstall the whole component + data are going to be deleted from your Joomla installation.
If the "complete uninstall" option is set to yes -> you'll loose all data! This action is irreversible. (unless you have a backup of the data)