If you ever want to delete any terms templates, you can do this by navigating to Library → Terms.
Then, click the three dots on the terms template you wish to delete → Delete.
Please note: You must have at least one terms template in your account at all times.
If you only have one terms template in your account and wish to delete this, you'll need to create a new terms template first and then set that new one as a default.
Please note: Deleted templates will no longer appear in the list. However, proposals that reference an deleted template will continue to use it until a new template has been selected.