If someone wants to change their Aadhaar picture, can they change it? Is there any limit to the number of times they can change their picture? What is the process?

Yes,  There is no limit applicable to the picture update on Aadhaar, if somebody want to change their picture on Aadhar they need to visit nearby Aadhar center and request for bio update and a fee of Rs 100 is applicable ,no such limit is imposed on the updation of picture.