Remove the plant from the pot. Gently remove all the old potting media. Wash off the roots. Trim off the dead and dying roots. Dead roots are the ones that are soft and brown. Live roots are firm and white. Select the smallest pot that the roots will comfortably fit into. Select the pot by the size of the root mass, not the size of the leaves.

Now is a good time to check for insects. See those black spots on the leaves? That's mite damage. Treat the plant as needed at this time and do follow up checks to control the problem.
Next: How Deep Do I put the Plant?