Note: Some will simply drain the existing fluid and replace it with new fluid.  While it's not the best of most efficient way to perform this maintenance, it still will work quite well.  If you want your cooling ystem to perform at its very best and maximum capability, the following information will then become very useful and very effective.  You can choose to what extent to wish to follow these guidelines....all, most, or part. 

Let's start from the very top:
First, it's easier if you begin by removing the plastic radiator cover.  You then need to only remove the drain bolt beneath the radiator to allow the coolant to drain out.  To rid the system of as much coolant as possible, once it seems to have drained, run the engine for just a couple of minutes and some additional coolant to flow out.

Next, regarding the little coolant reservoir located behind the side cover on the bike's right side, rather than removing it to drain its fluid, one can also simply use a good siphon to very easily and quickly empty the reservoir.

When flushing the system, you can very effectively uses a simple and cheap radiator flush: 

1.  Go to your local grocery store and buy "White Distilled Vinegar" and some "Distilled Water," mix those as a 50/50 solution.  

2.  Flushing the system now involves re-filling it with the 50/50 solution.  Know that it is not not necessary to remove the gas tank to do this.  Instead, remove the tank's two bolts (seen once your remove the seat) and then carefully and gently slide the tank back to where the radiator cap up front (towards the right side) is adequately accessible where a funnel can be used for re-filling the sytem.

3.  Run the bike with this solution until the bike is nice and warm, then let it cool, adding just a bit of throttle slightly above idling RPM. 

4.  Drain and then fill with 100% distilled water and run it through the system to wash out the distilled vinegar.  One can even take a "short" ride around the block, sometimes even better than it sitting there idling.  This is the same idea as cleaning your coffee maker.  The vinegar is acidic enough to remove any scale or impurities, but not so harsh that it will harm your delicate seals and gaskets.  The pure water then completes the flush.

5.  Fill with the new 50/50 premix coolant of choice.  PRESTONE EXTENDED LIFE 50/50 PRE-DILUTED COOLANT is excellent and reasonably priced and seems to be a favorite for our 1300. (Thank you, Jon.)  Engine Ice and a few other motorcycle-specific coolands are also excellent, but you can expect to pay much more for those, perhaps double, or more. 

6.  Run the engine and then allow it to sit for a few minutes, or again ride around the block and come back.  Check the level in the coolant reservoir and add whatever amount of additional coolant to the little reservoir that's necessary in order to raise the level up to where it needs to be.  (There are "full" and "low" hash marks seen on the outside of that plastic reservoir.  If you do an "oooops" and add too much coolant, that little siphon will once again come in very handy to extract it and put it back into the container of remaining coolant. 

Note:  It is "NOT" RECOMMENDED to use most automotive radiator "FLUSHES" as they are too harsh.

As previously mentioned, not everyone will go thru all of these steps when flushing the system, but if we are speaking of the ideal way to go about it, these would be the steps to follow.  And especially considering it's not very often when this service is required, the proper way requires only an additional 15-20 minutes of one's time and may be worth it.  Regardless, make it a habit to flush and replace the coolant every two to three years max, which will allow your cooling system to work more efficiently, last longer and potentially create one less concern down the road.