For future reference, you might want to post questions like this to the Project Management Central group as more folks would be looking there to help with such inquiries.
I'd suggest checking with your organization's PM policies & standards.
As Rami has indicated, the PMBOK would suggest that contingency reserves are within the authority of a PM to use to mitigate the financial impacts of realized risks (usually previously identified ones), but I've worked with some companies whose standards mandated that the PM would require additional approvals to access it. In effect, in those companies there was no difference between contingency and management reserves.
Another point I will make is that since contingency reserves are focused on risk impact reduction, over the life of a project it may be possible to return contingency reserves to funding sources based on the overall reduction in project risk profile. This ensures an efficient use of funding which would otherwise be tied up for the entire duration of the project even if most of the critical risks had expired much earlier.