How to extend m visa

Go to your local Chinese embassy/high commission and ask them for an extension.  If you overstay your visa, they won't be able to help you ever again, so much better to get this done way up front.  Too many people leave it too late.  It might take time, energy and even a little money in fees etc to get it done the right way, but trust me on this, it is worth it all.  I married my Chinese wife in the USA (I am an American citizen) and we had to get our marriage recognised by the city, the state AND the Chinese government which meant traveling around Vegas for a day after we got married to go to the relevant city and state offices and then going to San Francisco for two days to get the visa certificate authorized/recognized.  BUT upon our arrival in China we sailed through the visa process because we had the right paper work.  In any case, depending on where you are, you might be able to expedite things using a visa services company (there are a lot of them) but you will have to pay quite large fees.  Doing it yourself is cheaper but you have to visit yourself and be prepared to wait.  No way around it, I'm afraid.  The Chinese system is relatively simple but you have, like any country, got to do it the right way.