How do you stretch a lip for a 16 gauge lip piercing?

Assuming your lip was pierced at 18g and you want to stretch it to 16g, you must first wait the healing time suggested by your piercer. Then, wait a few more months and buy a piece of 16g jewelry and see if it will fit into your lip painlessly and without resistance. If it does, then you have stretched successfully! If not, wait another month and repeat.