Collision? Box Editing

Hi everyone, I am very new to all this and not even sure creating this in the correct place but have a simple question, at least I am hoping it will bea  simple answer. I was following the your first world tutorial but my rifle's blue box (assuming collision or something) got too big for unknown reasons to me so tried to figure out how to edit that but couldn't so wanted to use here to say hi and see if I can get a quick answer from the more knowledgable users.

 
Also, is there a way to lock the hierarchy window to not expand the whole object if I select some child on the scene. Thanks