How do I edit a project template used in Visual Studio?

I am using Visual Studio 2008 with C# and C++

I am doing some development on some code. The project uses an SDK that was put together by a 3rd party company that, when run, adds content to the options that is available when I create a new project or solution. When I use Visual Studio to creae a new project, the dialog box that comes up has an additional option in the column for "Project Type". In this tree structure ia a product that is from this company. If I pick this option, the right side offers a customized template from this compay.

The template creates a new project. I want to slightly modify this, if possible. Is it possible? Is it an asci file somewhere that I can edit. How do customzed project templates work in Visual Studio? How do I edit a project template used in Visual Studio? Is it an ASCII file somewhere?