If you don't know when the last time the coolant was changed, you should do it. The stock coolant in the radiator is good for at least 3 years, however the coolant in the reservoir should be changed yearly, because it can become oxidized. I change my coolant @ 3 years 10 months and under 24k miles. When I checked the specific gravity (boiling and freezing points), they were still pretty good.
Simple clean water will work fine unless the coolant system is badly scaled with lime, then a coolant flush that will not harm aluminum is recommended. Being that your bike is more than 5 years old , you may have some scaling.
I used Prestone 50/50 Ready-to-Use Prediluted Extended Life Antifreeze/Coolant that I had left over from my cars.
It's phosphate, silicate, and borate free and says it protects aluminum and all other engine metals and provide extended mileage or up to 5 years of protection.
This coolant is very light colored (yellowish) compared to the dark green OEM stuff.