You NEED and SHOULD replace the oil filter as well,also fill with the CORRECT oil and dispose of the old oil,a drive in garage i.e kwik fit,charlie browns,anywhere like that will do it as cheap as you can and save you the hassle,with due respect you should be able to find the oil plug if you have mechanical knowledge,it's on the sump,if it's not on the bottom it will likely be on the back.
a, March 2010