How do I download photostream pics (in the new Photos app) to my computer??

When I select the photos (in photo stream) that I want to export, I then go to File - Export, but all the options are grey'd out. When I right click on all the photos (I'm only selecting 4), no options to download or export. When I click on the icon of the square with the arrow coming out the top, there is no option to go to Shutterfly (my ultimate goal) or even to a file on my computer. It's like Apple does not want me to download my own photo stream photos to my computer! So frustrated.