When you want to delete a division, you may notice it doesn't want to let you do that. This is because there is a protection on it, when a division has a bracket or round-robin associated to it, or teams/players in the division, it doesn't want to let you delete in case it's a mistake you are making.
So basically you want to delete from the bottom up.
If you have a round-robin or bracket associated, delete those first.
Go to Menu > Manage > Brackets/Round-Robins.
Brackets or Round-Robins.
Select the bracket or round-robin.
Click on the Trash Can.
*If this tells you you can't delete, it it because there are matches created. If so, make sure you really want to delete this, because there is no going back. Click on Display More Options, click on Delete matches/Delete Opp. from Bracket/Delete schedules.
Then go to Go to Menu > Manage > Teams/Players.
Go to Teams (Or players if it's a singles division)
Select the division.
Select all the teams (Tip: Select one team and click Ctrl-A, this will select all)
Click on the Remove from Divisions (button along the top)
The system will ask you if you also want to remove all players (Say yes)
(This does not actually delete the teams and players but it will remove them from the division)
Now you are ready to go to Divisions.
Go to Menu > Manage > Divisions > Divisions.
Select the division you want to delete.
Click on the Trash Can.