You mean your user icon? That's very easy. Just go in Profile>Photos. There is a button with a plus sign in the top right saying "upload new photo". Click in it. Upload an image from your computer and then check mark "Make this image my user icon". Then it'll be your new user icon.
Profile, then to the right of where your name and stuff you like is, click on View More Photos, then click Upload New Photo. You then choose a photo from your computer and remember to check the box that says Make This My User Icon. Then click Upload.
Okay here are the steps:
1. Pick an Elsa picture.
2. Once you've chosen one go to profile.
3. Go to photos and click upload photo and upload it from downloads.
4. A button says make this my profile picture.
5. Click upload then there ya go finished.