It's the easiest method to add nicescroll to your wordpress powered site.
No hassle no fuss only plug-and-play plugin and you have a brand new and sexy scroll bar on every browser.
Plugin current version is based on nicescroll 2.9.5 release. (sorry, new version released soon)
Manually install plugin from administrator panel of your wordpress-powered site.
You can custom some aspects of scrollbar from "Settings" -> "Nicescroll".