If you are ready to try a transplant, this is what you will need to do.
Prep all of these things first before you start;
1. A 5 gal bucket 3/4 full with fresh 60-70 degree water
2. A 5 gal or larger flat tote or 5' x 5' piece of sturdy plastic
3. 2 5 quart ice cream buckets or equivalent plastic bowls, one filled with a mixture of 2 quarts 60-70 degree water and one cup of 3% H2O2 and one with fresh water.
4. Prepped fresh soil with a 25-30% perlite mixture
5. A scissors or trimmer with the blades cleaned with rubbing alcohol
6. A camera to document the process and take pictures if you run into anything that you have questions about.
Slide your hand under the canopy with the base of the stem between your index finger and middle finger to support the plant and pick up the pot. Working above your tub or plastic, turn the plant upside down, taking care not to bang or break the tops of the plant, slowly squeeze the pot sides allowing the plant to slide out into the palm of your supporting hand.
Once the pot is off, turn the plant back up and slowly break away the soil, you may break a few of the smaller roots but don't worry too much, its a weed and will recover.
After you have most of the old soil removed, its time to dunk the roots in the 5 gal pail of fresh water, hold the base of the stem with one hand and slowly massage the roots with the other until the all dirt is off. Once you have the dirt removed, inspect the roots, Pythium (root rot) will show as a brown, slimy sticky stinky mass, hopefully if you are unfortunate to have it, it is contained to the smaller hairy roots and not the bigger "leader or Tap roots". Try and leave those alone and wash it away, if you have to trim on them, do so only at the very bottoms.
If you do find root rot, and have trimmed away the bulk of it, then sit the roots in the ice cream pail or bowl of H2O2/water for 15-20 minutes keeping the stem and plant leaves out of the water. I use a piece of string tied at the base of the stem and to the pail handle to keep it out, if using a bowl, you may have to find something else to tie it to.
While the plant roots are soaking, prep your new container, if using the old container, clean it and the run-off tray well with a bleach solution. Fill the clean pot about 1/3 full of the new soil mix and make a depression in the center for the roots and still leaving a couple inches of soil at the very bottom.
After soaking in the H2O2 solution for awhile, gently massage the roots while in the solution and let sit for the last 5 minutes. Now transfer the roots to the pail of fresh water to massage and rinse them off, inspect for any remaining rot, your roots should be a light Tan to creamy White color when done. If you find any remaining rot, just snip it off and repeat the H2O2/rinse process until you are satisfied you got rid of most of it.
Now place the root ball in the depression you made in your fresh pot keeping the stem base about 1 inch below the top of the pot, hold it at the base with one hand and spread out some of the smaller roots around the bottom of the pot. add 2-3 handful's of soil and lightly compact, repeat until you are about 1 inch from the top of the pot.
Once your pot is full, slowly add some water, allow it to soak in a minute and add some more, as you water the soil will naturally compact, as it does, just add a handful of soil as needed but don't hand compact it, let the water do it for you. Once you get about 20% run-off, dump your catch tray and let them settle in.
I would try to plan this so you are finished up about an hour before lights off so the plants have the dark period to adjust, I would water with 1/4 strength nutes to start with gradually increasing with the next couple watering's. I would also recommend adding a beneficial bacteria to your watering's, I recommend Z7 but there is also Great White, Voodoo Juice, and other products out there, just make sure it is for soil/soiless medium and not Hydro.
If you do find you have root rot, you can toss your old soil, it is contaminated and the only way to kill the nasty's is to bake it in the oven which is a pain in the ass.
Good luck and if you have any questions let us know, taking a few pictures and documenting on your journal will be very useful information to others that stop by!