How to change your avatar 

Method 1: Changing your avatar by uploading a new one 

To change (upload) your avatar, click the edit option at the top of the 'About me' section. The edit option will become visible when you hover over that area.

On the resulting page, click the "upload new photo" button

In the modal that appears, click browse, and select an image. 
Check the 'certify' box 
Click upload 

The changes auto-save and a success message will appear briefly. 

Method 2: Changing your avatar if you already have an avatar in your profile avatar folder. 

To change avatars, simply click on your existing avatar.

You will be taken to your profile avatar folder.

Click the avatar you wish to change to 

On the resulting page, click "Make Avatar Pic" 

Click OK in the confirmation window 

A "photo updated" message will briefly appear. 

Other ways to change your avatar 

You can use any of your (non avatar) images and instantly turn it into an avatar. 
To use an image in one of your albums, click on the album. 
Follow the steps as in method 2: 
Click the image 
Click "make profile pic" 
Confirm the change in the confirmation window.