Well first you should download the image for your avatar, then go to your profile, upload avatar choose the image for your avatar and then after you upload refresh the tab, if it doesn't appear log out your account and log in again, if you cannot download and upload well you should check the pixel size image.
If there is a problem with the pixel size then you simply cannot upload the avatar image.
For the OP, you can refresh the page but as Aventhe said alert the manager and wait. You have the new avatar but it needs several minutes to be shown...
Edit : didn't pay attention to this necro topic...