how can I change to q visa after my x type expire and for how long I can have it?

First, you can try to change the X type to Q type at the local Exit and Entry Administration Department. If it the officer there says it cannot be done, then you have to apply for a Q type outside mainland China. Normally, if you can change it at the local department, it will take about a week. If you reapply for a Q type, it takes four working days for the processing.