While a project is still live you can cancel your pledge by visiting the project page and clicking the "Manage your pledge” button on the right-hand side. From there, click "Cancel Pledge" next to the "Change your pledge" link.
Remember, a pledge can only be cancelled while a project is live. If the project has ended and pledge collection has started it is no longer possible to cancel.
Additionally, during the last 24 hours of the campaign, it is not possible to decrease or cancel a pledge, without contacting our support team first, if doing so would drop the project below its funding goal.