Old Man Winter is a plasmid that's unlocked through the main storyline, so it's impossible to miss it.
Once it's been unlocked, equip it and press to use it on your enemies. If your aim is good, the enemy will be frozen solid for a few short moments. The easiest way to do this is to get up close for the freeze, and quickly pressing for a melee attack to shatter enemy.
Do this 5 times to unlock the achievement. You can reload the checkpoint, kill the same enemies, and they will still count towards the achievement. Purchasing both upgrades at a Gene Bank vending machine can make it easier, and would also unlock the 'Fully Equipped' achievement.