How can I Increase the breadth of a box ?

Please follow my instruction below:

– Add a new post
– At the bottom of content frame, look for “Custom Fields”.

– And add new Custom Fields with the following parameters:
+ Custom field name: grid
+ Custom field value: double

See the screen shot: http://imgur.com/qh08MCw

Regards,
Dominic

Please log in to Dashboard > Posts > open the “Screen Options”.
See the screenshot: http://imgur.com/WNJoHJ5

Regards,
Dominic