If you are coming from the Plugins screen, you need to click on the Deactivate button on the plugin tile labeled Kitchen Display.
If you are coming from the Manage Account section, you need to navigate to the Already Active section, on the Purchase Subscription screen, and remove the tick from the activation checkbox to mark the plugin as Inactive.
Upon deactivation, all the features and functionality added to the application are removed. However, you can always choose to reactivate the Plugin without incurring any additional charges, during its subscription cycle.
Note: Plugins in Tagrain are either Subscription Based or License Based. So the price that you pay for your plugins is based on the number of POS terminals that you have in your setup and the number of licenses that you have acquired.