Residence permit for China

My son left the UK August 2013 to work in China his contract ends on 30 June 2014. My son booked his return flight to the UK before he left for China and is expected to return on 1 July 2014. My son has just noticed his residents permit has an end date of 29 June 2014 which is 2 days before he is due to fly back. How does my son have this amended and will he have to pay.