You can edit a Role-based (Personalised) Public Form.
Steps
Select My Apps in the top menu
Scroll across until you see Contact Forms in the sub menu
Select Contact Forms
You arrive on the Manage Contact Forms page
Select Public Forms
You arrive on the Manage Public Forms page
Press the Actions Menu Button next to the Role-based Public Form you want to edit
A dropdown menu appears
Select Edit
You arrive on the Edit Public Form page
Reload the page by pressing CTRL+R (Windows) or CMD+R (Mac)
Make the changes to the Public Form that you want to make and then scroll to the bottom and press Save