You can change your reservation using the MyWheels app and on mywheels.nl. You can change the start time of your reservation up to the time it starts. Click on the time you would like to change and select your new start and end times.
If you want to reserve a different car, you can cancel the current reservation. You can cancel a ride up to the start time via the Cancel button in the reservation. There are no costs attached to this. Once the ride has started, you can only end it, cancellation is no longer possible.