You can tell if any piercing is healed mostly by the look of it and also how it feels to the touch. Is it still tender? If it still hurts to a minor touch, it probably is not healed. If there are crusts around the edges of the piercing and it is still leaking fluid, it is still healing as well. If your piercing is not leaking, crusting, bleeding or inflamed, I'd say it is probably healed enough to change the jewelry, but generally it is not completely healed until between 4 months and a year. Don't leave jewelry out of a fresh hole for long or it may close up, and I'd recommend having a piercer change the jewelry.