Photo event delete

You delete them by syncing again. Connect the phone to the Mac, open iTunes, click on the phone in the left pane of iTunes, go to the Photos page of iTunes and either remove the check mark in front of "Sync Photos From" (if you want to delete all previously synced photos from the phone) or change the selection of photos to be synced. Each time you sync with iTunes the non-Camera Roll photos on the phone are set to match the current settings on the Photos page of iTunes.