To edit your profile, including adding your profile's image, click the drop down menu in the upper right corner of your account and click on "My Profile".
To edit your profile bio, simply type in the changes and press save.
To upload (or edit) your profile picture, click on the "Photo" tab. Then choose an image from your computer to upload. Once is uploaded, crop it (if necessary) and then press save.
If you have any difficulty updating your profile, please don't hesitate to contact Udemy Support.