How to delete photo's from Siri's face in apple watch series 4 watch OS 6

They changed the location. As I noted in the above post, on your iPhone, open the Watch app and go to Clock, Siri Face Data Sources, and turn the apps on and off as you please.

That is no longer an option in iOS 6. This is the complete menu

Hey there dervatii,

Thanks for reaching out to Apple Support Communities. I understand you’d like to delete or remove photos from the Siri watch face. I’ll be happy to help with this.

There have been some changes with watchOS 6. With the Siri face, Siri takes a look at your day and displays information that’s timely and helpful. It might be your next appointment, the traffic on your way home, or the score of a game played by your favorite team, and you can tap to get more information. You can also turn the Digital Crown to scroll through your day.

You can customize the color and there are a number of available complications for this face. You can read more about this here: 

Apple Watch faces and their features

Cheers!

On your iPhone, open the Watch app and go to Clock, Siri Face Data Sources, and turn the apps on and off as you please.