Save to your computer in the large size.  Come to a group. Click on Upload Photos in any album. Select all the photos you want to upload (and resize)  At the very bottom of your screen on the left, you'll see Resize Photo, click on that. It will give you 3 resize options.  Choose one and click Upload Photos.  This will resize them and upload them at those smaller sizes.  The originals will stay large.  Then just go to the albums and save them individually at the smaller size.  Save as something like this:

 

original file name:  babynewborn.jpg

save smaller version as:  babynewbornSM.jpg

 

hope that helps!