Modifying the template only removes the fields from your data entry screen. It has no effect on your printed invoices. If you are using Peachtree First Accounting, it does not support using Templates. If you are using any flavor other than Peachtree First Accounting, a Templates button appears at the top of the Sales/Invoicing screen beside the other buttons such as Save or Open.
If you want to modify the printed invoice appearance, you can do that no matter which Peachtree flavor you use. You do that under Reports>Accounts Receivable. Click the Invoices folder and click once on the invoice form you want to modify. Then click the Design button and make and save any desired changes.