How do you modify Page Template?

All code will be in the template. That is how custom templates work.

Altering the output those templates is a code edit except where the templates have been written to include the post body, or meta fields, etc.

But don’t go to Appearance->Editor and start hacking away. First, if this isn’t your theme you are going to have to redo the work when you update the theme, and second, if you make a mistake in the built in editor you can take the whole site down and not be able to get back in to edit the file. I consider that editor the equivalent of working on an airplane while it is in the air.

Instead, grab the file via FTP, edit it is a text editor, preferably one intended for code, then reupload it. Ideally, you’d set up a development server on your computer so that you can not only edit but test the changes before pushing them live.