I have tried everything, but I can't change in to my Masquerade ava .that I bought. It's unboxed.

[rainsom]

I also bought a school uniform earlier and it's not showing up in inventory. Begining to feel I wasted my money :)

[Rolig Loon]

When you buy an avatar, it often involves wearing several parts, the same way that you would wear several articles of clothing to make a complete outfit.  If you opened the box and saved its contents to your inventory, you should have a folder with all the parts in it.  Just wear (or add) each of them.

Your uniform may be in your Received Items folder, way at the bottom of your inventory.  If not, double check in your Marketplace Order History to be sure that it was actually delivered.  If not, and if you were charged for the purchase, contact the merchant and ask for a redelivery.  Be sure to include all the details of your purchase (cut & paste them from the order History), so that the merchnt knows exactly what you should have received.