Right, a change to an earlier flight on the day of departure. The last time I did this it was at the airport and as you rightly say no charge for easyJet Plus members. At that time I had to pay (IIRC) £20 to have my son transferred to the earlier flight.

You should be able to do this online or via the App. You will see the charges payable before you are committed to the change. I think the fee for non-Plus members is now £42 and as you say, save for the change fee, there should be no repricing of the fare.