Url Injection

Yo.
So I just realized there are a lot of blogs who’s indexes can be accessed via going to /wp-content/uploads . Which basically allows you to access all of their hosted content. How can i protect my site so that people can’t do that? I thought it’d be something with apache or something, but yeah. I don’t know what to do to block this type of attack. I want to add a 403 error (whichever ones like that page cant be accessed by the likes of you).
Help?!