The spark plugs can be removed through the sides, behind the side fairings. You do not need to remove the gas tank to get to them on the 2008+ Ninja 250R's. You can either use the 16mm plug wrench, or the wrench that in the included tool kit (16mm, part #92110-0044).

Wrench size: 16mm (part #92110-0044)
Torque specs: 115 lb
Gap: .07-.08mm (.03-.04in)
Spark plugs: CR8E or U24ESR-N


How to read your Ninja 250R spark plugs? Here's a good illustration:
http://dirtbike.off-road.com/dirtbike/data/articlestandard/dirtbike/232006/332655/4.jpg

i was told you can look at your spark plugs to see if your running lean. If so, what would you be looing for?

Lean = less fuel = can lead to overheat

Also, too wide of a gap will make it harder to spark and you'll have problem at high RPM. Too close of a gap will wear out the plugs quicker. The spark plug gap will slowly expand as you use it, so just follow the recommended service interval to check it. Oh, don't forget to add in anti-cease compound when our torque the plugs back in.