You will have to resize the image.
There are several sites which do this for you online, such as http://www.resize2mail.com/
Another way is to download some free software which can do this as well. A suggestion would be Irfanview
. It displays many different file types and offers a resize feature.
As a last resource you could use Windows' very own Paint. Open the image in Paint, click on Image > Stretch/Skew and fill in a percentage lower than 100 for both horizontal and vertical. (if it's still to large, you can repeat this step