yep, as what enter said,
you can enlarge the picture, but it will result in a more blurer and pixelated picture

in fact, it's best that you NEVER resize your picture from small to big, if no choice, make sure its not bigger than 110% of it's original size, else you'll see weirdand ugly artifact/pixelation will come out.

solution : trace and make it vector,and enlarge it at any size you like
1. adobe illustrator
or
2. macromedia freehand