Hi Donna,
It may possible to remove the root and not kill the tree, however this should first be inspected by a certified arborist to ensure no harm comes to the tree. If the arborist determines the root is not essential for stability, then the root may be removed by digging up the soil around the root and making a clean cut. A root exposed to soil can create a pathway for insects and disease to enter the tree, and care should be taken to ensure this does not take place. 
Arborists are certified through the International Society of Arboriculture, or ISA. ISA maintains a search engine that makes it easy to find a certified arborist in your area. Give a few a call, and hire the one that most appeals to you. Ask for references for good measure. A good arborist should work with you, and explain each step to be sure you know the procedure and risks. 
You can find the ISA search engine at the link below:
https://www.treesaregood.org/
Thank you,
-Julie