Work Visa and Work Permit Will Expiry in May 2014

Hi

I have been working in Beijing and i have finished at my old Job, And Have a New job my work Z will Expiry in May, and my work permit how do i go with changing my work permit job name to the new job. Would i need to go through the whole new process again? and The Work Z would i need to leave the country and come back again?

Thanks