Word of caution: Coolant needs to be non silicate and compatible with Mag alloy engines. Read their labels. Silicates kill the seals and you will get pump failure.
Not teaching anyone to suck eggs but, the right way to drain all coolant is the drain bolt on the water pump, you will need a new copper crush washer. The bleed screw on the left handside of the bike is for air bleed, then rest of the system is air bled and fed from the main rad inlet.
Since the service manual says change after 3 years I would say it's a time based change. You will be fine for 6 months yet, I've had my original coolant in 3 and a half years now with no issues. But will be changing it next week.
Having done this today thought I would provide my 2 cents on what I learnt.
Service manual does state 2.5l but despite my best efforts I managed only 2.2l - 2.3l. It states to leave upright when filling but does not say what position to drain but obviously, it's more effective lent on the side stand.
Removing the water pump drain bolt, air bleed bolt and reserve tank siphon hose will allow it to fully drain properly. Once drained I poured half a litre of water in to wash away the dregs. Replenishing the system used almost exactly 2l and the reserve tank a further ~250ml.
I found it difficult to locate the siphon hose initially but it's actually very easy. At the bottom of the reserve tank, left side, probably hidden behind several other hoses. Once pushed aside you should see it clearly. Images below for reference. I used Putoline Ultracool 12 coolant, I also have 700ml left if anyone UK based wants it to save buying a third bottle. Pay postage and it's yours! 👍🏼