If you got you hands on any of the pre-order bonus outfits or from ResidentEvil.net you can unlock this achievement right away:
As soon as you gain control of
Rebecca hit
for you inventory. Hover over to
Personal, right next to your weapon. Press
and use the option
Switch. It will show a
Suitcase icon now. Then pick
Use. Now you should see the costume/T-shirts option screen. Choose any other outfit and confirm with
. The achievement unlocks when you gain control of your character again. It did for me at least!
Update:
Team Wesker costume - Unlocked after completing
Wesker Mode (unlocks after completing the main story game once.)
As for further costume unlocks I might update this solution when and how to get them. Just need confirmation.
Hope this helps!