I have several plants in my home and when I go to re-pot them I'm finding a lot of small worms, I use merical grow for them no other potting soil. Where are the worms coming from and how can I get rid of them????

Could be larvae or small white springtails which could be in the bag of soil your using. I have heard of people opening up a brand new bag of soil and having fungus gnats fly out.In either case, let the soil on the plants dry out more if you can since they like to be around moisture.
If you don't like chemicals, try a little soapy water at watering time, or, you can try flushing them out over the sides outside to either get rid of them or keep their numbers down and replace any soil lost. Maybe even another brand of soil might be in order.