Can't remove SHIMANO Nexus FC-C6000 Crankset
You need a crank puller.  It threads in to the crank arm, and presses on the bottom bracket spindle to pull the arms off. 



http://www.parktool.com/product/crank-puller-for-square-taper-cranks-ccp-22

A video here from Park Tool on using their crank puller: