Change Value based on Dynamical Object

Goal:
The goal is to make the variable with value '2014-06-14 09:00:00.000'

Problem:
The syntax code is created as a dynamical object how do you make it from '2014-06-14 16:20:10.000' into value '2014-06-14 09:00:00.000'?

DECLARE @a datetime = '2014-06-14 16:20:10.000'