If you're getting a picture from an external source ('EXT1') it suggests that you've got a Freeview set-top box plugged into the set. If so, you'll ned to use the remote control for that box, rather than the one for the TV set.
If you've not got a set top box in use (and you've got an aerial plugged directly into the TV), have you actually carried out a scan of all available channels? (You need to do that, in order to get the channel information stored in the set, before you can select individual channels).