On one of my Television in the kitchen, we have a FREEVIEW set top box receiver. There is a message on the Channel Five station informing us to retune our receiver. I would appreciate some more information and the reason for the change and how to go about it. I went to the Channel Five website and found nothing there to help me. Really appreciate some help here.

You need to go into the menu of your box and find the tuning options and rescan the whole thing.
Some stations/channels have moved bands and so a retune is required.

In some areas, one station or so has continued to broadcast in standard definition announcing the change.

After the DTV change took place, stations changed their physical assignments.

You can think of DTV as having virtual channels and physical channels. So, virtual channel 6.1 through 6.5 could be assigned to physical channel UHF 17 before the switch and re-assigned back to physical channel 6 after the switch.