Applying new template to existing PP presentation

[Ron]

I'm using a pp 2003.

I have an existing PP presentation that was created with custom template. I
had the template modified very slightly. (just changed the background image).

How do I apply the new template to the current presentation?

I tried using the apply template design but it just uses the first title
slide template for all the slides, instead of using the template title slide
for the first slide and the slide design for the rest of the slides.

Thanks, Ron