I just changed my oil yesterday. I bought oil and filter from newspeedmaster.com . It also came with the drain plug gasket.
I didnt warm the engine but its a good idea. I opened the drain (I think it uses 13mm) socket and let it drain into the pan. Then I loosened the oil filler plug (you can use a wide plier) to make it drain faster. Wait until it empties and barely drips.
The toughest part was removing the original oil filter. Its on pretty tight. I used an oil filter wrench but you probably could do it by hand. Make sure you have the pan under there too.
I lubed the rubber ring on the new oil filter and filled it with oil. Then screwed it on tight with a regular wrench. Put new gasket on drain plug and tighten as much as you can.
Pour the oil in all 4 Liters. Plug oil filler and tighten.
Run the bike and check for any leaks. Stop engine and check oil level.
