So in the image below there are two circles, how can I remove the internal vertices between them without messing up the outside shape. I'm working on a gun and this is just a simple way to illustrate the issue I'm dealing with. If I where to go in and delete the internal faces it would leave holes on the outside of the object, is there a fast way to get around this?

[![Red area shows internal geometry](https://i.stack.imgur.com/Q3hpU.png)](https://i.stack.imgur.com/Q3hpU.png)