In your SMS.to account, in the Send SMS in your menu tab, please select Templates
Once you click on Templates, a list of your saved templates will appear. Choose the template you would like to Edit/Delete. Once you have selected the template, on the bottom right, please click on the 3 dots and the Edit or Cancel option will appear.
You can then go ahead and Edit or delete your templates.
Please be sure to save your changes once prompted to do so.