There are multiple ways to resize an image. This is typically done with graphic editing software however there are a number of tools which enable this to be done without having to be a graphic artist.

 There is nice one available with windows XP from http://www.microsoft.com/windowsxp/Downloads/powertoys/Xppowertoys.mspx

Alternatively try using one of the freely available image resizing websites available, try this search on google http://www.google.com.au/search?hl=en&q=online+image+resize&meta=