Well, I drained about 200-300ml by unscrewing slowly the drain bolt...well, I thought I would just let it drip a little, but no, the damn thing wouldn't drip until completely off. Guess what, it dropped in the oil pan, and I stuck my index finger in the whole to stop the oil from leaking out (good I had nitrile gloves and the oil was not too hot..)...
I somehow managed to screw it in, and as a result I discovered that I drained exactly as much as I had planned. So far, so good.
I took the bike for a ride, and now I have this ticking noise, which is most pronounced around the 4k RPM in 3rd gear, but it's there in all gears, just can't hear it so much. I swear, it was never there before! Also, there's 2.8 litres of oil in the engine, right now it sits on the top of the marking on the dipstick.
Needless to say, I'm confused and worried...