My Site getting Spammed spammer creating blog post which i want to delete all blogs

My Site getting Spammed spammer creating blog post which i want to delete all blogs, is there a way to delete all blogs of all users at once ? also is there a way to turn of Blog feature, i have capthca enabled also user needs to upload photo to sign up een inspite of it spammer creating profile and blog every second, so first want to delete all blogs of all users and want to turn of blog feature