Twitter doesn't have a built-in feature to delete media posts all at once. The best free way is to go to your profile, open the Media tab, then press F12 on your keyboard and paste the Twitter Media Deleter script into the console. This script will automatically scroll through and delete your media one by one, all you have to do is keep the tab open. Another way is to use tools like Tweet Delete or Circle Boom. Their free plan allows you to filter media and delete them in bulk, but the free plan is usually limited to 100 to 200 tweets per month, so you'll have to do this a few times.