Changing Pictures in Themes

Big thanks to anyone willing to help. I downloaded the wordpress them wp-gold, and having some issues that are really setting me back.

I was simply trying to replace a picture in the theme, (the header), and did so by opening it in photoshop, altering it, then re-saving it with the same exact name.

Now the picture isn’t showing up at all?

I’ve never had this problem before since it was such a simple task.. Any ideas.

Thanks