If you need to repot a plant, there are a few important things to keep in mind so that the process is the least disturbing possible for the plant. If you do it carefully, you'll be rewarded by healthy growth from nutrients and knowing you got rid of salts.
1. Water the plant a couple of days before you repot it so that the soil is moist when you're ready to work on it.
2. To remove the plant, slip your hand over the top of the pot and hold the plant's stem, then turn the pot upside down.
Tap the pot against a hard surface, then slowly pull the pot away from
the plant. After several tries, if the plant still doesn't come out, use
a knife to cut around the edge of the soil. If that doesn't work, you
can break the pot. If you happen to break some of the roots, don't
worry. There are times when a plant's roots are pruned to keep a plant
at a smaller size, so breaking off a few roots in the replanting process
won't hurt anything. In fact, if the plant has become rootbound (roots
tightly curling around the sides and bottom of the rootball), it is
important to slit through the sides and bottom of the rootball to
encourage the roots to branch out into the new soil.
3. Remove about one-third of the soil.
4. Put a few inches of potting soil in the bottom of the new larger pot (no more than about 1 inch larger in circumference than the old pot), put the plant into the pot, and make sure the soil level is high enough so that the soil line on the plant stem isn't above the top of the pot. The soil line should be about 1" below the top of the pot. If it's too low, add more soil below the root ball.
5. Fill in around the root ball with soil, tamping the soil
down hard around the edges of the pot with the tips of your fingers or
your thumbs. This removes any air pockets that could dry out the roots between waterings.
6. Thalassa Cruso, a plant writer and guru wrote that it's a good idea to thump the potted plant down hard against a firm surface just to settle the soil and encourage the roots to get busy and grow.
7. Soak the plant until water runs out the bottom and then let it drain completely.