Adjust the pledge and each pledge payment.

To change the fund, use the adjusted fund field on the Adjustment tab of the Adjustment record.  If the pledge was split to multiple funds, use the Split Gift tab of the Adjustment record.   
To change the campaign, use Campaign field on the Split Gifts tab.  

Note: any future payments will reflect the corrected campaign and/or fund.

Note: To change the designated fund for a posted pledge, and update the designated fund for future payments only, refer to How to apply a pledge to a different fund halfway into the pledge schedule.