I don't have the image in a large 300 dpi format, which is what I need. I have a smaller one that I upscaled, but you can tell when you print it - it's not as clear as I'd like. I got the small image from Shutterstock I think (or one of those places) and I can buy the images from them for what I need if I want the large 300 dpi version.

Photoshop definitely is available as a software package. Best way to learn....hmmmm....really a combination of things. The idiot books aren't a bad starting point if you've never done any graphics work. I have their book for Illustrator, their Photoshop book is probably pretty similar. There are a lot of online tutorials out there as well, but the real best way is to just start using it. Some stuff you'll figure out quickly, other stuff takes time. Photoshop is probably the premier non-vector based graphics program out there, pretty much everyone uses it. If you're doing a lot of graphics resizing, a vector based program such as Illustrator (both from Adobe) is good to have.

It also depends on what you're wanting to do. I use Photoshop a lot for pure graphics work, I use InDesign for building publishable quality material (always in conjunction with Photoshop), and Illustrator on a rare occasion. So depending on exactly what you're wanting to do graphics wise, Adobe probably makes a software package to do it.