How to convert single entry to a multiple entry VISA

Dear Sir, I have come to the Chinese Embassy and applied for a multiple Entry VISA on 2nd February. I was directed to go the Le Meridian hotel that I complied and applied for the VISA. I was not in possession of the Support letter from my friends at the time of application but have the document with me now. Please help me with converting the single Entry Tourist VISA to a multiple Entry Visitor’s VISA before my planned departure to China on February 27th 2012. Please help me with the required application process that I will comply with and follow up.
The details are as follows:
Name: V Pinnamaneni
Date of Birth: 24Feb1944
Issue date: 02FEB2012

Thanks for your help