You can edit the existing lists with the following steps:
Android
- Scroll down the left sidebar.
- Tap the Manage Lists & Tags button at the bottom.
- Tap the list you want to edit.
iOS
- Swipe left on the list name in the left sidebar.
- Tap the Edit icon to edit.
Other platforms
- Right-click on the list you want to edit in the sidebar.
- Click Edit.