You'll need to use a picture editor program in order to "re-size" the image, and preferably "save it to a jpeg format for further compression. If you don't have anything appropriate on your computer, you could download
GIMP, which is a GNU licensed proggy, and usually does a good job. The one thing about it is, when you open a bitmap file (bmp), you'll have to use the "Export" on the "File" menu to get a jpeg (jpg) file, since Gimp wants to save in its own format. You could then either upload to here, once you get the size down, or upload to another web site and link to that here.