problem with upgrading to sap jco 2.1.7

To upgrade to latest sap jco, I need to replace the old

librfc32.dll from c:\winnt\system32. But when I am trying to delete or overwrite this file, it is saying like access denied and sharing violation respectively. I tried doing the same by closing all the windows and then rebooting.But still can't delete or replace the librfc32.dll file. Can any one of you guys help me regarding this?

Thanks,

Sridhar