Officially - use a proper flywheel puller designed for the purpose.
On the other hand - this is the method I have used for YEARS but do so at your own risk...
Unscrew the flywheel nut and remove any washers, starrter cup if fitted, and anything else that is loose. Replace the nut so it is FLUSH with the end of the crankshaft. Have an assistant use a lever behind the flywheel and lever it in the direction of OFF. Firm sustained pressure is all that is required. Now - either directly, or with a steel drift, strike the end of the crank DEAD SQUARE with a hammer. The flywheel should pop off easily.
If you have a Briggs & Stratton engine with a starter clutch fitted to a long crankshaft extension, use a close-fitting deep socket over the end to protect it and hit that.
phil_saunders(a)bigfoot.com
Phil Saunders
May 2011