Hello, im so sorry this is a late reply but if you haven't found out how or anyone else who looks at this thread here is how to change your leagues name (Note: You may only change a league name and 3 letter acronym once so choose wisely!)
1) Make sure you are the league marshal or your league marshal is the one who sends the request to change a leagues name
2) Send support a ticket asking to change the name of your league, include the new name clearly and new 3 Letter acronym if you choose to.
3) wait for reply, they will probably ask for a confirmation telling you that you may only change it once, this is when you reply and make sure its the name you like
Note that this may take a couple days up to a week so please be patient when the devs are getting back to your ticket :)