Regulo has beaten me to it.
Normally, if someone reported only receiving a limited number of channels on Freeview my first response would be to ask them to check that they're actually in a Freeview reception area. (Some parts of the country still aren't):
http://www.freeview.co.uk/availability/
Then I'd suggest that they'd probably need to upgrade their aerial installation.
However, if the only channels you're receiving are exactly the same as the principal four analogue channels, it suggests that it's because you're actually using an analogue tuner. While, as Regulo states, all new TVs can receive Freeview (or, for certain specialised TVs, FreeSat instead), many also have the ability to receive the older analogue channels.
You need to get the handbook out and look for the bit (probably somewhere under the 'Menu' settings) where it tells you how to switch between analogue and digital reception. You've almost certainly got the 'analogue' setting at the moment. Switching to 'digital' (and possibly retuning as well) should fix the problem.
Chris