iCloud backup not backing up from photos mac

Question

I've paid the extra to store my photos in iCloud, I seem to have two libraries and despite trying to change the backup to the larger library it isn't backing up the set of photos I want. I've tried changing the settings in iCloud in System Settings. Does this feature work and if so how do I change backup sets?

Answer 1

The answer is to replace the whole photo set with a new photos library which Apple support talked me through creating. Then switch the backup set in the preferences of Photos. I also used Powerphotos to merge the redundant sets to check that I hadn't missed out on any stray shots.