If you increase (or decrease) the price of a Service, any existing, upcoming appointments for that Service will remain at their original rate. Any new appointments for that Service will be booked under the new rate.
There's no need to cancel or rebook any existing appointments if you'd like for them to be under the new rate as well. Edit each individual appointment, reselect the Service, and reselect the duration. Reselecting the Service and duration will update the appointment to the new rate.
To learn how to edit a Service, click here.