We put September 2013 in order to give us enough time to get things right, but our goal is to actually deliver it sooner without breaking any promises or dates. We want to put the best product possible together and take the time to do so, and we feel it will actually come together quicker, particularly with the support we are receiving here, but we don't want to fall short of expectations.
Visit the project page and click “Manage Your Pledge.” Enter a new amount in the pledge amount box. Note that you are not adding to your existing pledge; the amount you enter will be the total amount collected if the project is successfully funded.
http://www.kickstarter.com/help/faq/backer%20questions#HowCanIChanMyRewaSele Visit the project page and click “Manage Your Pledge.” To change your reward, make a new selection. Note that changing your reward selection does not automatically change your pledge amount.
These guidelines are borrowed directly from Kickstarter's official FAQ's.
Don't see the answer to your question? Ask the project creator directly.