If you've got a 'normal' TV (which could receive Freeview transmissions if you'd got a terrestrial aerial) together with a Freesat box, this applies:
Your TV should be set to take its input from the Freesat box (probably by setting its 'Source' option to something like 'HDMI1' or similar).
Channel selection should then be by using the remote control for your Freesat box. (i.e. you're effectively using the TV just as a 'monitor' to display the output from the Freesat box. It's not really working as a true 'television', which actually handles TV signals).
-------------------------------------------------------------------------------
If you've got a special 'Freesat' TV (which doesn't require a separate Freesat box) then, obviously, channel selection will be directly via the TV set's remote control.
-------------------------------------------------------------------------------
Now we've established which remote control (if you've got more than one) you should be using, here's a list of the channel numbers:
http://www.insidethex.co.uk/xmltv/lineups/List_of_channels_on_Freesat.html
You'll see that the Regional' options allow you to choose which BBC region you want directly from the Electronic Programme Guide but that the same options don't exist for ITV. That's because ITV's licence to operate (granted by OfCom) prohibits them from providing a service outside of the UK, meaning that they have to use satellite beams which are far more tightly focussed than those used by the BBC.
Somewhere in the initial set-up of your Freesat box (or Freesat TV, as appropriate), you should have been prompted to enter your postcode, which should have set the box/TV to recognise the correct ITV regional beam. So you need to look for a way of changing the postcode entry.
Alternatively your Freesat box/TV should offer a 'manual tuning' option, so that you can enter the correct frequency and polarity for the region which you wish to receive (using the details in the table here:
http://www.stevelarkins.freeuk.com/itv_regions_sky_digibox.htm )
If you need help changing the postcode and/or manually tuning, we'll need to know the make and model of the relevant Freesat box or TV set.