Follow these steps to change your profile pic (avatar):

• In the top-right, click your avatar to open the menu. Select 'Photos'
  

• You'll see your recent photo's, click the '+' sign to upload a photo.
  

• Select an album for the photo (or create a new one) and select the photo to be uploaded.
  

• When you've uploaded the photo, you'll be back in the photo overview. Click the photo you've just uploaded.
  

• Here you can click the person-icon in the top-right to 'Use as profile photo'.
  

• If wanted, you can crop the image, and then it's done!