Sponsor of my mother -change in marital status/witdrawn of co-signer

[Reimer19]

Hello,
I'm a Canadian permanent resident. I applied to sponsor my mother under the family class option, she lives in Peru. My application was received by the CIC Office in June 2007. At the time that I submitted the application I was married to a Canadian citizen who served as the co-signer and who helped me reach the Minimum required income (LICO).
We separated in December 2007 and officially divorced in May 2009. He decided to withdrew his support for the sponsorship application of my mother.

I'm now able to financially support my mother without my ex-husband support.
What is the next step? Do I have to let Immigration know? Would the change in my marital status affect my mother's application? Even though I make more than enough money to carry on the responsibility of being her sponsor? What type of letter I should send to CIC? Do I fax any information? or mail? What information should I send to CIC?

I appreciate any information you can provide me. Thanks!

Reimar