People often ask me about repotting orchids. It's really very simple. What follows is a little narrative of the process. Our volunteer for the day is Paph. Wossner Goldegg, who I've shown photos of in previous posts. For reference, paphs do appreciate being repotted yearly.
Start by grooming dead leaves or inflorescences from the plant. Water the plant, since damp roots are more flexible, then give the pot a squeeze to loosen the roots, then knock or pull (gently) the plant from the pot. Hang on to the pot for the moment.
Clean the old media away from the roots. If there are bits stuck to the root, don't bother to try to break them off. This just results in unnecessarily injured roots. Take this time to assess the quality of the roots. Paphiopedilums naturally have tan to brown hairy roots with yellow growing tips. They should be firm and plump. If you find any that are squishy or dried up and crispy dead, you can go ahead and gently pull them off, or at least pull off the outer covering and leave the little wiry true root in the center. Watch out for the growing tips - ideally you want to make sure they don't get damaged.
Now select a pot for the plant. In general, people often go with a pot that is just big enough for the roots. This prevents the occurrence of too much wetness in the pot for extended periods, which leads to root rot. Often this can mean putting the plant back into the same pot it was just in. You can see from the photos that this would work with this plant. Sometimes it can also mean going down a pot size if the roots were in trouble. Don't be afraid to do this if it will be the best thing for the plant. And of course sometimes you might find you can't easily get it back into the old pot and to put it up a size or so. In this case, even though the roots just fit in the old pot, I think they could fill a very slightly larger pot just as well, plus I tend to underwater so the plant will likely not get damage from a soggy bottom.
Next of course is to fill in the pot with an appropriate media. Nature of potting media can vary considerably from person to person and plant to plant. Basically, we don't use "regular potting soil" because it stays wet too long. For paphs, most people use some pine bark or coconut husk chunk based mix (these are NOT mulch) with other additives. Also generally the bits are small, about 1/4 inch unless you're dealing with a very big plant. I prefer a coconut husk chunk (chc) mix with sponge rock, diatomite, charcoal with some organic fertilizers added. I mix my own, but if you only have a few plants you can buy mix from other growers, or sometimes get ok stuff from the hardware store.
Backfill the pot with media, gently tapping and poking it down between the roots. Tamp it enough with your fingers that it becomes reasonably solid, but not so much that you squash the roots and all the air pockets. With paphs, bring the media up to just above the bottom level of the base of the leaves, maybe 1/4 inch, so emerging roots will be protected.
When you're done, the plant should be solid enough in the pot that you can gently pick it up by the ears and it will not come out. Be careful, this obviously will not work if there are not enough roots to anchor the plant, or if you've potted into a clay pot, or if you've used a heavy media such as for hydroponics. Incidentally, unless you're dealing with a rather large plant, I wouldn't recommend using clay pots for paphs. They dry out too fast.