Making a Form Template inactive will not delete the template but remove it from the Active Template list so that you are able to reactive it should you need it again. This function is only available within the Web Portal and not available within the App.

To Deactivate a Form Template in your Web Portal > Forms > View Form Templates > Select the Template/s you would like to deactivate > Select Deactivate from the pop up menu. 

How do I Reactivate a Form Template?