The most correct way of doing this is damaging your durability to zero, and repairing with lucky time, the item will loose maximum durability each repair. Lucky time is supposed to happen the most when the item looses its maximum dura thus upgrading the quality of the item.
after you've upgraded the quality of your item, its also known that items with less maximum dura are easier to upgrade in TC so you wont be failing as much mets as originally, at least on your first upgrade till it returns to a higher maximum durability