First time Ive done this on new Vectra so thought Id share
Here it is...
* Take your car for a quick spin to warm engine oil up
* Jack front end up (or if your lazy like me, sling about 3 flags down both sides and drive up onto them :-)
*Loosen the oil filler cap and disptick
* Put newspaper all over underneath of engine on floor to protect YOU WILL GET OIL ON THE FLOOR!
*Locate the sump plug, if you look from behind the front wheels the sump plug is central towards the rear of engine compartment at bottom, plug points at 45degree angle down - put at least 5litre oil bucket underneath to catch oil
*Use 45 hex socket to loosen sump plug then undo by hand, careful when oil first starts coming out not to loose sump plug. Leave 30mins for oil to completely drain.
*Locate oil filter, put another tray underneath to catch small amount of oil
*Use 24mil socket to undo ( i did this by reaching down from top)
*Unscrew oil filter cap, pull out oil filter, replace with new oil filter paper element (4 prongs on the outside) screw back up to 25nm and wipe away excess oil that has dripped onto other engine components
REMEMBER TO CHANGE THE RUBBER SEAL ON THE OIL FILTER CAP WHEN REPLACING - about £1 from dealers
*Replace sump plug and new o-ring, I just bought new sump plug from dealers, cost me about £1.50 and came with o-ring, I know its not damaged then. Tighten to 10nm and wipe away excess oil
*Clean away all newspaper and oil from underneath car and lower car
* Fill up about 4litres of oil then let car run for a few mins ( if oil light comes on then top up a little more)
*leave to settle for 5mins then check oil level and top up last bit as necessary, I put in mine about 1l more at this point.
*Check underneath for leaks then all done!
Hope this helps...