Replace “?s=” with “/search”

Hi all,

Few days back while i was configuring my newly installed blog, i saw some option where i had been asked whether i want the search URL to be like “?s=” or “/search”.
At that time i didn’t notice this and ignored but now i am in great need of it. I am not sure where i saw this option, somewhere i some plugin or some configuration of wordpress blog only.

Any pointer to my problem will be greatly appreciated.
I want to change my search now to “/search”. I had already tried the plugin “google custom search” and it didn’t worked.
Plz help.
Thanx