You can change your profile picture on Demio using Gravatar.
Gravatar stands for "Globally Recognized Avatar," and is used often around the web. It's basically an avatar (or profile picture) that's connected to your email address, so that your picture is synced across all of the sites with which you use that email.
Demio uses Gravatar, and so in order to change your profile picture on Demio, you will simply need to go to https://gravatar.com/ and create an account with the same email address that you use for Demio. After creating the account and uploading your desired profile picture on Gravatar, your profile picture on Demio will change.