...
To edit a List that appears in a Contact Form, Event Creation Form, Event Guest Booking Form or Survey, go to the Lists App (steps described below)
To change which List is used as the set of answer choicesin a Multiple Choice Survey Question, go to the Goals App and follow the steps to edit a Multiple Choice Tracker. But if you want to simply edit an existing list, go via the Lists App (steps described below)
Steps
Go to My Apps in the top menu
Select Lists
You arrive on the Manage Lists page
This displays the Lists that are owned by you or your organisation
From here you can click the Edit button next to a List to edit that list
When you click edit you arrive on the Edit List page
...