Niko

I have an XT660R, the oil change is very simple.

The best advise I can give you is to use the owner's manual, it is clear, detailed, simple to follow and gives you all the required torque settings.

the pressure switch is not touched in anyway during an oil change!

For an oil change:

replace the crankcase drain plug oil washer
replace the tank drain plug oil washer
if you change the oil filter, you do not need to change the oil filter rubber ring unless it is damaged.

Unless you use extremely cheap oil and change frequently, I recommend changing the oil filter at every oil change (yamaha oil change is at 10k km)

If you follow the owner's handbook routing, then it is quick but don't rush it and let the old oil drain.
You check the level after the oil is at full operating temperature, say after a ride. wait 2~3 minutes and check the level: unscrew the dipstick, wipe it and then put it back in (loose) without screwing it in (very important). hold the bike upright (vertical), make sure you don't tilt it towards the right at all. Hold it for 5~10 secs, then remove the stick and check the level
et voila