Smaller width in entry-content

Hi, I realize the entry-content ID are smaller inside multimedia than other menus, like Profile, messages, etc.

How can I setup the same width in Multimedia than other menu option? I tuck screenshots but new users can’t upload…

Thanks in advance and best regards.

Hi, I tuck screen capture to show better what im referring.

http://www.than-sad.es/Files/Width.jpg

Any help or tip will be really appreciated.