visa china, venezuelan passport

Hi, it's possible for you to apply for an extension 7 days earlier before it expires within China. You can try it! If it can be done, you don't need to leave China.
You should first prepare your passport, valid registration form of temporary residence, the application form, a passport-style photo, and an invitation letter from your business partner, as well as the return ticket. And then submit the application to the exit and entry administration of the local PSB to apply for the extension.

I need to be at least 6 months in china

Usually, the extended period won’t exceed the duration of stay of your current M type. If your current one's duration is less than 6 months, I'm afraid you cannot get it. Anyway, you can try. Good luck!