how to delete photos from apple watch

In the settings for Photos in the Apple Watch app set the limit to 25 photos (no idea why this can't be set to no photos), and select album that contains no photos (I have selected Favorites which I don't use).

Not saying it will help you, Apple screwed this up so much that deleting all media and all 3rd party apps may no longer free up enough space for the update.

To remove a photo from Apple Watch, open the Photos app on your iPhone, then remove the image from the album you've synced. To create a new album for Apple Watch photos, use the Photos app on your iPhone.

To delete photos off your watch you delete them off your phone.