New to Booking

Hello. I have just joined booking and I have already listed a property. 

I have a problem. Could anyone please help? 

I uploaded some.photos with the property and the site has automatically chosen a main picture to display to potential clients. 

However, I want to change that photo. Delete it and actually upload a different photo to use as main...I cannot delete it, and I cannot chose another photo as main. How should I Proceed? 

Thank you