The nut comes off with a 14 mm or 15 mm socket (not sure which). A lot of cheap crank pullers come with one. For example:
Crankset Crank Wheel Puller Removal Repair Extractor Tool For Mountain Bicycle | eBay
If you're in a hurry, don't order a crank puller that has to come from China, though. They can take a while to arrive.