To remove the oil cooler, you should do that first drain engine oil and coolant. Next, unclasp the hose clamp and unconnect the coolant hoses from the cooler on the rear face of the sump. Then, undo the bolts that hold the cooler to the sump and recover the o-ring seals when the cooler is drawn out and be ready for spillage of fluids. For refitting, make sure that the mating faces of the sump and oil cooler are clean, and then refit the cooler with new O-ring seals and tighten the retaining bolts securely. Reconnect coolant hoses and hold in place with new clips where needed, and finally, fill up the engine oil and cooling systems.