In order to start the procedure of changing your driving licence; you need to make an appointment with your doctor for him to issue a Health Certificate to be used when changing your licence. The doctor will charge you approximately DKK 350.00 for the certificate.
Please note that you should take a separate passport photo to the doctor for the above meeting. There are very strict rules in regards to the passport photo. For example, if you wear glasses, the frame must not in any way cover your eyes, a shiny forehead or shiny cheeks are not allowed, if you wear a veil; eyes, nose and mouth must not be covered (find guidelines in Danish, but with useful illustrations here