If you go up to the search bar and look up repotting you'll find a wealth of posts that show what to do with those roots. Anything that oozes water when you pinch it needs to be removed. Cut back to healthy root. There is a whole process to go through if you find evidence of black rot. If anything is seriously black...refer to the posts about antifungal treatments with Physan 20 and other treatments such as Hydrogen Peroxide. Good Luck, I've just gone through weeks of repotting due to a similar problem that spread from an affected plant.