Only the creator of the album can change the settings, here's how:
1. Go to your group's homepage.
2. Click on "More Group Options" in the blue drop down menu on the right.
3. Click on 'Photos.' in the blue tabs.
4. Click on the album that you want to change the setting.
5. Click on 'Edit Album'.
6. Change the settings for 'Who can view this album' and 'Who can add photos'.
7. When you are finished, be sure to click 'Edit Album'.