Editing templates is a process similar to creating templates. There are two ways to edit a template.
For templates you have created yourself, or templates that are not locked, you can add or edit fields as you would do when creating a template initially. (In a locked template, the fields are all grayed out and not clickable.)
If you want to edit a locked template, you will have to duplicate the locked template. To duplicate, click on the second button next to Template in the editor.
Once you have duplicated the template, rename your duplicate and assign it a different URI.Then click Create.
After you have created the new template, you can change fields, add fields, or delete fields.