How can i extract a shape in photoshop?

I would like to take a shape, this one, to be exact, and enlarge it.

I'm planning to use this as a wallpaper on my computer, but the image is such a low resolution that it just can't be done nicely. But since the image only really is some basic shapes, I was wondering how to get those extracted to fit the occasion (make a larger resolution image). And by extracted, I mean something along the lines of using the magic wand tool to select the shapes and then filling the selections with black to make it higher res. Sounded great in theory, but the edges of Vader's biceps (whole Vader in fact), became very pixel-y.

If anyone could help me out I'd be forever grateful!

BR,

Pontus.