Can you help me with my visa extension?

hello Sir,i am from Nepal.i am from Nepal.My visa expiry date is 28 august 2013.i am going to China on 1 august.Could you please tell me can i extend mine.if yes the its also twice of each period of one month ?for this where i should go and it should be done before how many days.please answer mw ASAP Sir.i am so worried ,please help me Sir.looking for your reply.thank you Sir.