There are two ways to do that.
1. Right click on the picture, left click on "save image as" (or some version of that), save it on your desktop, then open it there. Your scroll wheel can make it any size you want.
2. Right click on the picture, left click on "properties", copy and paste the address into your browser, open it and a left click on the picture should make it bigger.
I prefer method one as it is faster and easier and get you the biggest picture.