Option 1- Download the entire gallery
Click into the Collection that you want the gallery from
Select the Gallery tab
Click Export Media
Choose what you want to download. If you need both, simply click Export Media again and then choose the other option. They should both start to export to your computer in a Zip file.
Option 2 - Add someone as a Collaborator
Select the Collection you would like to invite the Collaborator to
Click on the Invite Collaborator link
Add in their First Name, Last Name, and Email then click "Invite".
Giving someone Collaborator access will allow them to view and export the user gallery, while not having access to anything else on the Collection or Account.