Note: You need to have both an Xbox Live Gold membership and a THQ account for this.
Begin by going to any clothing store and pushing . Click on 'Character Gallery' towards the bottom of the list and you will be asked to log in to your THQ account. Once you log in, click on 'Upload' and once it's finished leave the store.
If the achievement didn't unlock, try going to the main menu, clicking 'Community', log into your THQ account and then repeat the steps above. This time you will not be asked to log-in when you are at the clothing store.