Downloading: This example assumes that you are using Microsoft Windows. There are other ways to do this. If your way works, you don't need to change it.
At the bottom of the photo (in blue), select the size of photo that you want to download. 
Wait for the new size to load (if you changed it).  NOTE: If you select "original", do not be alarmed if you only see a portion of the picture, just because it won't fit on your screen doesn't mean that you should not download it. The original is great for printing and/or cropping.

Then, right-click in the photo area, a menu will pop-up. 
Select "Save Picture As..." and the "Save Picture" window will pop-up.
Select the destination location on your computer and rename the file as desired. Click the "Save" button and your done.