Display post date as 04/26/2013

the_time( 'm/d/Y' );

or

the_date( 'm/d/Y' );

Note, the_date() will not print the same value twice. If a second post would get the same output you get nothing.

If your theme doesn’t set a fixed value, like Twenty Twelve …

get_the_date()

… then the format is taken from your settings in Settings/General Settings:

enter image description here

You can change the format here, no need to change the theme.