There is a special puller. However, if you are real careful, it you use two large screwdrivers (one on either side of the flywheel), you should be able to gradually work (wobble )it off.
Before you do that, you should check to see if your serial number is in the range listed on the Honda website for a flywheel recall.
Honda Marine - Recalls and Product Update Information
THIS IS A SAFETY ISSUE.
If it is in the range, contact your dealer immediately to see if it have been changed. If it is in the range and has not been changed (and you are in the US), it will be changed out at no charge...no matter how old the motor is.
Mike