If I went on a tourist visa can I extend it once I'm there and settled?

Hi I've been asked to come to China by a friend who is living there, he mentioned a teaching jobs are available and pay around 8000 a month, a couple of questions are I have dds that I would need to keep up in UK is that enough to send about £150 back a month? If I went on a tourist visa can I extend it once I'm there and settled? Any help with this would be appreciated many thanks :)