Once a league has been generated (written to the diary) then the number of fixtures and the teams cannot be altered.
The fixtures can only be moved to different dates/session/rink.
The names of the teams and the members in the teams can be changed freely.
There are 2 steps to deleting a league, but you cannot begin to delete a league if the league has any results/scores entered. So first you must manually delete all entered scores in the league, before following the next 2 steps.
If it has been generated, go to the league's Fixtures page and scroll to the bottom where you'll see a red button for Clear fixtures from diary. If the button is not there, one or more matches have a result entered.
Once that is done, or if the league is not generated (same thing), Edit the league, and at the bottom of this page is a red Delete league button.