Locate a growing pot that is only 1 to 2 inches larger in diameter than the previous pot. Peace lilies generally prefer crowded conditions, and need transplanting only when the roots begin to take over most of the soil.
Place a piece of broken clay over the drainage hole to allow the soil to drain thoroughly.
Pour a sterile potting mixture into the growing pot to fill it halfway full.
Set the peace lily pot on its side on top of newspapers. Grab the base of the plant firmly, and gently slide the spathiphyllum out of the container.
Remove as much of the loose soil as possible without damaging the peace lily roots. Place the roots into the new growing container so that the peace lily sits at the same height as it did in its previous container. The root ball must sit within 1 inch of the pot rim.
Fill the growing pot with more soil. Press the soil around the peace lily plant gently.
Water the soil until it drains from the holes in the pot. Never allow standing water to sit under the pot.