My bike didn't come with a toolkit either so I just used a standard socket wrench with a extended socket and took my time. If you remove the gas tank it makes it a lot easier. I have similar socket tool that came with my set to bend it around the tight spaces but I just used an extender to get it around the frame and that seemed to work fine. Take your time and don't overtighten the plugs and you should be good.
http://faq.ninja250.org/wiki/Changin...rands_to_avoid