Ok. I write here because you can actually keep this window open paralel to where you'll be working so that you can follow the instructions step-by-step at your own paste.
1. click on your av in the upper right hand corner of the normal play window. The Preferences panel will pop up.
2. Where it says Change Avatar click on the grey Browse button. From the list find and click on your old saved av. Click on Open in the lower right hand corner of that same window. The window should disapear.
3. Click on the blue Upload button next to the Browse button in the Preferences panel.
4. Wait a few seconds and hit F5 to refresh.
Hope all goes well.
