If you’re an iOS user: tap on the 'Overview' tab on the lower left corner of the app, then tap on the Goal you'd like to edit. On the top right corner, tap on the three dots, then tap on the 'Edit Goal' option.
If you’re an Android user: Select the Goal and in the top right corner, and you will see there's a pencil icon.
From here you can update your cover photo, the name of the Goal, the target amount, what Rules are applied and who can save with you.