Just remove the orchid from the pot, gently remove the old growing medium and repot with fresh medium. If you leave the old medium you could cause root rot as it decomposes. These orchids don't grow in soil in their natural environment, but their roots are exposed to moist air. This site has lots of info including how to repot.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.