X visa not changeable?

For the X type, I would like to change it to an F/L type. Does that mean that you simply can't have a different visa without leaving China or does that mean that when you change it, the old one becomes invalid and everything is based on the new one? I need an extension because I booked my airplane ticket for 1 year on the basis of the course I subscribed to but the X type was is fact only valid for 11 month.