With the most recent update, Samsung removed the icon for remastering a photo. It was simply nestled directly under a photo. Now, you have to hunt for it. If you are already aware, then you're way ahead of me. But, just in case...
1) Tap the three dots in the upper right corner of a photo.
2) Tap on details. Once you've opened details, the remaster button should appear, and now master away.
