As long as an update has not been posted about an update, you can edit a Progress Tracker.
If an update has been posted using that Progress Tracker, the tracker is ‘Locked’
Steps:
Find the Progress Tracker in the Library
Click the Actions button on the right side
In the dropdown, select Edit
You arrive on the Edit Progress Tracker page
It resembles the Create Progress Tracker page
Make the edits
Press save
You arrive back in the Library