Can I delete a photo once uploaded?

Yes. Login to your account and go to the Manage Photos tab under Account Settings. Find the photo you want to delete and click ‘Delete photo’.

However, due to the nature of the license, once a photo is released under CC0, the license is permanent and non-revocable, which means that your photo can continue to be used by the public (though it won’t be available on the Unsplash website). For more read the Creative Commons FAQ on the CC0 license.