Need to cancel?  Not a problem!  See how below, 

On the web:

• Go to the bookings page on your account.
• Click the edit booking drop down. 
• Select 'Cancel Booking'.
• Click 'No thanks, I'd like to cancel my booking'.

In the app:

• Tap the bookings icon on the bottom left of your screen. 
• Tap into the booking you want to cancel. 
• Scroll down to the cancel booking button and tap. 
• Tap 'I'd like to cancel my booking'.