How do I choose or change the cover image of an album?

In the album's edit page, under the design section, there's an "Album Cover" row with a Change button next to it. The cover is the big image guests see at the top of the album page, so it's worth picking a strong shot — usually the couple's favourite frame, or a wide shot that sets the tone of the event. You can swap it any time, so if you find a better frame later in the editing process, it's a thirty-second change.