keep the bike level and remove the drain bolt from the crankcase. Leave the adjacent banjo bolt in the crankcase, do not remove that. The oil in the crankcase should come out now.
on the lower rear of the oil tank there is a bleed bolt, just like you find on a brake caliper. Shift a piece of fishtank hose on the bleed bolt and give the bleed bolt half a turn. The oil in the oil tank should come out now.
After the bike has stopped leaking close the bleeder bolt, and install the drain bolt again (with a new crush washer please).
Put the bike on the sidestand, and remove the oil filter cover to replace the oil filter element. And bolt it up again.
Now it's time to put new oil in the engine. Fill the oil tank to it's neck with oil, and start up the bike. let it run for 15 second and kill it. (really important!!). Fill the oil tank up again until you have poured 2 quarts in total into the oil tank (which is slightly below 2 liters) . The engine and oil tank together are claimed to hold 2,3 liters of oil, but we don't want to overfill.
Fire up the engine, and let it warm up. Ride around the block and let it idle at least 1 minute until the fan comes on. Kill the engine and check the oil level. Add oil untill the oil level is the top mark on the dipstick (measure this with the dipstick not turned into the tank)
According to BMW, you should measure the oil level with the dipstick screwed in. This is just dumb...
Unscrew the oil cap. Wipe oil off it. Then screw it back in, then unscrew and check to make sure the oil level is between the min and max lines.
Note: Some early versions of the users manual shows the max line in the wrong place. The max line should be just next to the "M" in the Max. User manuals after March 2007 should be correct. See service bulletin 00-011-07 (027) from May 2007 for more information.