Business visa extension

Hi, currently I have a business type for 6 months and it expires on July, I know it's too anticipated but I probably plan to stay longer in china. So I'm wondering if just before it expires I can extend/renew it. I don't care if I have to go out of Mainland or the kind I get as far as it lets me stay longer. And if so, does anyone know any agency who can do this for me, or it is easy to do it by myself? and it is very expensive?
Thanks so much!!