If you need to tweak a little bit more and don't want to install anything new. Just open the picture file in MSPaint, once the picture is open just choose the "Image" option from the top tool bar, then select "Stretch & Skew". Keep your Horizontal and Vertical percents the same when reducing the size, like 50% and 50% and it should shrink your pictures down easily.
Not nearly as easy as right click and re-size to some defaults, like with the power toy image tool but you do can see your changes while your making them. Image tool is easiest if you know the default size your looking for.
Try them both!!