are you keeping the sky or replacing it with freesat, is it a standard freesat box or the new pvr box.
the only reason i ask is the answer will vary somewhat as to what you need to do.
but if its just a case of swapping a standard sd sky box to standard hd frresat box (non pvr) its just a case of connecting your satellite feed to the freesat box, then connecting the box to tv via hdmi then running the set up/channel scan on the box then your good to go.