You can edit any record you've entered into eBird by clicking the "My eBird" tab and then choosing "Manage My Checklists." Then click the "View or edit" link next to the checklist that contains the erroneous record.
On the checklist page you can edit the existing effort information by clicking on the "Edit data & effort" link.
You can also delete an erroneous species by clicking "Remove Species" next to the species name. If you don't want to delete the species, just edit the numbers or notes associated with any species on the checklist, click "Edit Species List" at the top of the species list.
On the edit checklist page, you can use "Change Species" to move photos or sightings to another species, and also edit any field that's associated with your checklist. Hit Save when you're done, and you're good to go!