There are several ways you can resize an image, and it all depends on what programs you have and what you want the end quality to be like.
The simplist way to resize an image is in Paint. Just click on the select tool (the little rectangle at the top of the toolbar) and make a box around your image and then pull the little blue squares inwards (or outwards). The problem with resizing in Paint is that there may be a noticable loss in image quality if you resize it by a significant amount.
With better programs, like GIMP and Photoshop, you can use the scale tool (I don't know if it's called the same thing in PS...) to resize it and that'll keep the quality a bit better than Paint does.
Or you could just make a post in the
Digital Request area and get someone else to resize it according to your specifications.