As of Mid 2019, the users with the "Template Manager" permission are able to delete parameter templates.
Prior to this it had to be managed by DM Support.
Contact DM Support to have this permission enabled if you require it - it is needed to be able to view and delete templates as per the next steps.
To delete a template:
1. Go to Parameter Templates in the toolbar in OEM
2. A list of templates will be shown - Click Delete to the left of the template to Delete a template.
If a template is already in use by a device, OEM will not allow you to delete it.
To find all devices using this template, go to the device list in OEM, and filter the list - this will show which devices have the template applied. From there you can either apply a different template, or simply Edit the device parameters individually and save. This will mean the template is no longer in use on the device, and can be deleted.