Templates cannot be deleted…..You can unassign all branches and I suggest you change the name of them to InActive or Do Not Use

Thank you, David 

I don’t see any options to unassign branches or change their names. Perhaps I don’t have that privilege or it’s in another location. 

Can you direct me to the settings for this please? 

Go to Admin>Estimating>Opportunity Templates

Open the template(s) you wish to edit

Edit the Opportunity Name field to InActive

In the Branch Assigned field delete all branches

I also highly suggesting changing the name to something like “DO NOT USE” like  David mentioned.