I'll show you an easy way to delete a template, arogers.
Once we've deleted an invoice template we can't retrieve it back. I'll show you how to delete it:
Let's log in to your QuickBooks account.
Click the Gear icon at the upper-right.
Select Custom Form Styles.
From the list, click the drop-down arrow under the ACTION column.
Select Delete and click the Yes, delete this style option to confirm.
We'll still be using the deleted template to the transactions we previously applied to since QuickBooks won't retroact. We can open the transaction and toggle it to a different one. Just click the Customize menu at the bottom and select a new one. If you need help with customizing your forms, check out this article for more details: Customize invoices, estimates, and sales receipts in QuickBooks Online.