How do I delete a post I uploaded?

I saw that the site lacks of a feature that allows users to remove or definitively delete a post if, for the reason you want and say, we regret of doing it...

It'll be deleted automatically after three days if no one approves it

Only users with approval powers get to delete posts. This isn't going to change. There are very few circumstances in which it is acceptable to circumvent the standard process for post deletion, and allowing ordinary users to do this would be an invitation for abuse.

Also, uploading a file to this site doesn't give you ownership over it. You can't delete posts you uploaded, because they don't belong to you.