I believe what you need to do is complete IMM 1436 and submit it.
http://www.cic.gc.ca/english/information/applications/guides/5218ETOC.asp
This is the "Request to Amend the Record of Landing, Confirmation of Permanent Residency, or valid Temporary Resident Documents".
Sounds like it must happen periodically, since they have a form and an instruction book for it.
Good luck!