Today PHP version 5.4 is needed some how on Debian Squeeze and after a little bit search on web I decided to update whole system to Debian Wheezy. By default, Debian Squeeze come up with PHP 5.3. Also it is possible to work with 5.4 on Squeeze but it needs much more effort to upgrade (I tried to compile PHP and failed). Anyway, Below procedure is successful to upgrade whole new Debian system.
Before starting, take your back-ups and your own risk :)