How to delete custom template

Good afternoon, @mmay.

QuickBooks Online has a Custom Form Style feature. Let me show you where to locate it:

1. Go to the Gear icon.
2. Select Custom Form Styles under Your Company.
3. Click the Drop-down arrow next to Edit.
4. Select Delete.
5. Click Yes, delete this style to confirm.

I've attached a screenshot below:

Also, you might want to check this article on how to customize invoice emails.

Let me know if you have any trouble finding this! I'll be around.  Have a great weekend!