I think the C260 is just a facelift of the C250. If it is, you access it through the removable cassette compartment. blue thing in top right hand corner. use pliers to remove the spring clips on the pipes then feel up the sides of the pump and there should be two springy plastic lugs, squeeze them to release them from the support and pull.
pump comes out still attached to wiring.
refitting is simply push back in until you hear a click.
edit, actually,thinking back I think it might just have been 1 springy lug to release it.
The 260 is located in flush tank beneath the flush circuit board.After peeling off the overlay and removing the board you will see it.The previous model 250 the pump came out of the bottom of the tank after emptying it.They changed the pump to inside top of the tank so that it drains properly and does not crack with frost as previously.