Changing the dates format

I have data in these two formats 7/13/2014 9:24:14 AM and 07/12/2014 13:02. I want them in Am - PM style. I tried date , there is no format which suits my requirement. The first format in excel is general and other is custom under dd/mm/yyyy hh:mm . Please assist. I have 23k rows, which I cannot afford to change manually.

Is this what u r looking after ?

Punnam

Hi Punnam,

It's just the opposite of what I need
I need all the dates in 24 hr format.