Deleting HSDL Templates

I am trying to manage the number of spreadsheet templates within an environment. When on the 'Spreadsheet Templates' page, I am using the orange drop down on the right hand side and can see there is an option to 'Delete' but this is greyed out. This is the same whether the template is in 'Draft', 'Active' or 'Inactive' status.

Can anyone advise the steps required to delete the template?

Thanks!