If the WC suite is a very old one and screwed to a timber floor, unscrew and remove the pan's fixing screws. Then, taking the pan in both hands, pull it from side to side and away from the wall. If the connection to the soil pipe is made with a mastic or putty joint, the pan outlet should come easily out of its socket (which will have to be cleaned of all jointing material before the new unit is fitted). If a rigid cement joint has been used then there's usually no alternative but to use a bit of force.
This means deliberately breaking the pan outlet, just behind the trap and above the pipe socket, with a club hammer. You can then prise the front part of the pan away from the floor using a cold chisel and hammer. This will separate the pan outlet from the pipe. At this point it's a good idea to stuff a bundle of rags or screwed-up newspaper into the drain socket to prevent any debris getting into the soil pipe.
Next attack the socket to remove the remains of the pan's outlet. For this, use a small cold chisel and hammer but do it carefully to -avoid damaging the drain socket itself - this will be used again. It's best to keep the point of the chisel pointing towards the centre of the pipe.
Try to break it right down to the shoulder of the socket at one point and the rest will then come out fairly easily. Repeat the chipping process to remove all the old jointing material. Remove the bundle of rags or newspaper with the fragments of pipe and jointing material. Then with your cold chisel, remove every trace of the cement base that secured the old pan to the floor.