Heya Hound
You're planning to cut it back on top too I hope?
Here's how I do it:
1. Take clones. If plant is too sickly to clone, cut back growth by 1/3, choosing mainly thick, low branches and their new growth to remain if possible- cut off the spindliest, lamest looking third, basically.
2. Prepare your soil and have it on hand.
3. Let teh plant get a bit dry
4. Upend it and support the rootball so it doesn't fall apart as you slide it out of the pot. Take a bread or serrated knife and carefully saw off a diagonal slice of the root ball. For a plant in a round pot, I leave a half-moon shape of soil on the base and slice up a wedge up the side of the root ball, taking about 1/4 of the total soil mass.
5. On the other side, scratch the roots low down to the bottom edge of the pot that you did NOT cut off so that they are just a tiny bit loose. Don't overdo it.
6. Pour some fresh soil into the pot while it is tilted so that the shape of the fresh soil leaves an exact spot for the plant. Put some fresh soil in the bottom, too.
7. Put the plant back in the pot. It SHOULD be slightly higher than it was, and there should still be a small amount of space around all sides, whcih you can then backfill with your fresh soil.
8. Water lightly with a fert solution (I use a bloom formula) at 1/4 strenght.