Radflush, it's not expensive, and will clean up the waterways like you're descaling a kettle.
Perfect temperature to do it as well, just empty out your system first, replace the bottom bolt, pour all of the bottle in then top up with water.
You can then either let the bike tick over on the centre stand for about 15mins (if you're lucky you may even hear the fan kick in), or take the bike for a good blast.
Either way, once done, empty the system and also flush with a hose.
After that refill the bike with coolant, making sure the overflow expansion tank level is correct too, and then you're all done.