What is the best procedure to achieve a smaller lower half of the face? (Photo)

Great question!  Yes a buccal lipectomy can help improve your facial shape by shrinking down the lower cheek region.  By doing this, the jawline and the cheeks become more defined and contoured.  Another treatment to think about is Botox to the posterior jawline as this will also help slim the face from a more squared to a more oval appearance on the frontal views.  However, it is always best to have an in person consultation with a board certified plastic surgeon so that your goals are reviewed and the best treatment recommended.
Best of luck and hope this information helps!
- Dr. Roger Tsai
Board Certified Plastic Surgeon

Patients who have a very round face even at normal low weight could benefit from cosmetic plastic surgery procedures to slim down the lower haft of the face. 
Buccal fat removal corrects the fullness pf the lower anterior cheeks ( chubby cheeks). It makes the face to be more V shape and less round, specially when smiling. 
Botox treatment to the masseter helps to decrease the fullness of the lower posterior face, thus complementing the results of buccal fat removal. THis helps to achieve a more devined V shape lower face. 
Chin liposuction removes the double chin. When it is performed along the jaw line too, it helps to have a more define jaw line. 
The video below helps to understand who could be a candidate for buccal fat removal.

Based on your photos, you seem like you could benefit from a buccal fat pad removal procedure and possibly Botox to your Masseter muscles as well. These procedures can provide slimming in the lower face. I recommend consulting a board certified plastic surgeon with specialization in facial aeshetics in person to discuss your options.Hope this helps,Ali Rıza Öreroğlu, MD FEBOPRASEuropean and Turkish Board Certified Aesthetic, Plastic and Reconstructive SurgeonIstanbul, Turkey