Here is your tutorial to make this job. Please, follow all instructions
Please, go to: IMAGE IMAGE SIZE (or ctrl + alt + I)
Size: change on the "Pixel Dimensions" to 1800 (pixels) on the small size (width or height). Please, must to keep the proportion on the other size.
Photo final size (after retouch): (+ -) 1,0 MB
Size: 30 cm (centimeters) on the big size. Please, must to keep the proportion on the smaller Size. Only change the big size, the smaller will be the proportion.
Crop the image between the mouth and the chin.