If you cant remove it via changing browser settings and your homepage keeps changing back to Bing.com then it may be a virus called 'Search with Bing'.
If so, there is some useful info detailing various steps to attempt its removal, located at:
http://malwaretips.com/blogs/search-with-bing-removal/
Malwarebytes anti-virus removal package is a good option to try to remove it initially, which if you do not already have it installed you can obtain the free version at:
https://www.malwarebytes.org/mwb-download/sem/. Make sure you select the option to install the free version only.