As long as you have a release on Apple Music/iTunes, you can go ahead and sign up for Apple Music for Artists.
If you're just out to update your artist profile picture you can contact our support team with the following information:
Link to your artist page. If you don't have one yet, send us the UPC(s) for your release(s) instead.
A square JPG or PNG file with a minimum size of 2400 x 2400 pixels.