If your project hasn't yet received any pledges, you can take it offline from your dashboard. If you have a look at the options down the right side of the page, under the heading 'Manage your project' you'll see 'Take offline' in the list.
If you click that, your project will go back to draft mode. You can then edit things like the target, duration and funding method and relaunch the project when you're ready.
Get in touch with our Crowdfunding Support Team if your project has already received pledges.