Meteor Accounts Add Extra Fields

How do I add extra fields to the Meteor Accounts?

Ex: Profile Picture, Header Picture field etc...

I know how to change the password Accounts.setUsername(userId, username); But how would I add an extra field to the Accounts?

You need to update the users collection in mongo. The way to access it is by using

Meteor.users.update(Meteor.userId(), {
    $set:{
        profile: {
            picture: 'url-to-picture'
    }
}});

According to documentation, anything that need to be updated by user should be stored under the profile key

profile: an Object which the user can create and update with any data. Do not store anything on profile that you wouldn't want the user to edit unless you have a deny rule on the Meteor.users collection.