10 year 60-day Visa change to 10 year 90 or 120-day

Hi, I have a 10 year 60-day one. My travel agent back in the states did not inform me that their were 90 and 120 day options. I am in China for a year, but would like to cut my traveling costs down. I am wondering if I am able to change my 10 year 60-day visa into a 90-day or 120-day one. whether I do that in China or in Hong Kong. Is it possible to switch? Is there a fee to switch?

Best Regards