Are you working from a laptop, @Alessandra945 ? If so, then, yes, go to Booking Settings. Scroll down past Guest Requirements and House Rules until you see Policies. You will see Check-in Window, Checkout Time, and Cancellation Policy. Beside Cancellation Policy click Edit. Choose the policy from that dropdown that works best for you. Right now I see yours is set to Flexible.
If you are working from the phone app, it is under Booking Settings as well, and you just select Cancellation Policy.
Hope that helps and you get it set!