It would have to be 2 transactions in order to do this. Cancel the old one. Book a brand new booking which will have a new booking number.
Does your current booking have a refundable deposit?
Also, check if the new booking deposit will be refundable, before you proceed.
Also, if you have promos connected to the old booking, you’ll lose those. Compare those to what promos you’ll receive with the new booking. Any OB purchases, etc will be refunded, when you cancel and you’ll need to repurchase them in the new booking.