need space on watch to download update

Delete them off the phone.

Choose a photo album and manage storage on Apple Watch - Apple Support

My watch says there are 18 photos in the about section, but it is synced with an album containing 3 photos. How can I clear down the 15 to get enough space to upgrade please?

I tried syncing with an empty album but it still showed 18.

I have no additional apps on my watch - I have cut the photos in the synced album to 2 and am now showing 17 photos in ‘about’.