A lot of camera software comes with resizers, my canon s/w has the tools to resize one or bulk resize a bunch of photos.
Some email software can resize.
Google 'resize photos' for a boatload of free/shareware tools that will also resize a shot.
You can also use a jpeg quality reducer to make the picture more 'compressible' without losing the resolution that resizing does. If its a shot with a lot of the same color, like an animation shot or a picture of a lot of water or sky, that may work well. If its a highly detailed shot, not so much. I think "paint" or "microsoft photo" had an option under 'save as' to reduce the jpeg quality, which in turn brings the size down. This is like shooting with your cameras 'regular, fine, superfine' options.