You must have the Advance Portal activated to allow constituents to change their pledges.  You can check the status under Portal Status Info and should see a blue button labeled "Deactivate Advanced Portal" if you have the Advanced Portal.

• Select Pledges from the list of menu options.
• Turn the toggle Allow to Change Pledge Schedule? to YES.
• You can also include up to 5 email addresses to receive notifications about pledge changes in the next field for Email Addresses to Send Pledge Updates To.