New software called parkREG was installed on Wednesday.
During the day, car park staff were on hand to assist users to ensure there were no disruptions while the upgrade was carried out.
The new 'pay as you like' system means that online users of the car park are required to re-register their details so they can continue to use the service.
Cllr Phill Bicknell, cabinet member for highways, transport and environment, said: "I would like to thank everybody for their patience while the changes were made to the system."
People who are registering for the first time or are re-registering will be able to take advantage of discounted parking charges until the end of October.
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