How long can I renew/extend my 'L' tourist visa for?

I'm an Indian citizen currently in China on an 'L'(Single Entry, 90 days from entry). I will be visiting the Exit and Entry Management Section in Beijing with a renewal form. I will be renewing the 'L' visa, but would like to ask for multiple entry and increase the desired date of validity. Can this be done? What is the maximum number of days that I can extend it until?