Unfortunately we don't yet have a way to edit the price upwards in checkout. Instead we suggest either:
Increasing the price of the service in the booking form, which you can do by clicking on a booking to surface the modal and then clicking the 3 dots and ‘Edit Booking’:
This will open the booking window on the right where you can click on any of the services to open the service drop down. Then simply click on the price box and type in the higher price:
Save changes and proceed to checkout as normal.
Or you can create a service called ‘Extra Charge’ or 'Long Hair Charge' in any of your categories for £5 or £10 and add that as an extra service at checkout: