Its extremely easy, just remove the oil sump plug and the little plastic piece inside it (use a 6mm allen key) - let the oil drain, remove fill plug from side of transmission and add required quantity of oil plus 1 litre slowly keeping the drain open, drain the extra 1 litre oil and let it trickle down so there is only some oil coming out, put back plastic piece and sump plug, The required oil will be correct and fresh.