Hello Florence 48, and welcome to the forum.
First, I'd wait until it's through blooming to repot. It's OK to repot when they're in bloom if they really need it, but I think your plant will be fine if you wait a bit.
These orchid roots need light and air to do well. The main reason to repot is because the bark medium breaks down over time. It then packs down, retains too much water, and slowly suffocates those wonderful green roots.
When you do repot, start with a clear, plastic slotted orchid pot, just a little larger than the current one. The clear, slotted pot helps air and light get to the roots.
Get some new bark, there are various choices. I like just plain medium bark chips, I add a couple of small river rocks to add some weight to the pot. Some growers add other ingredients, choose what works for you. Moss can be used, but is more difficult to manage watering, in my opinion.
Unpot the plant, and rinse off all the old medium. ONLY cut off roots that are clearly dead, black, mushy, slimy. If they look a little iffy--leave them!
Put the plant in the new pot, work the new bark in around the roots. I use a chopstick to help.
New bark holds less water than the old, you may have to increase watering for the first six months or so.
Then proceed with good care so it will bloom again for you!
Care is different than for other houseplants, but they're really not difficult.
Please post again if you have questions.
