In ConfigMgr packages on a Distribution Point are placed on the drive with most free space. Sometimes this can be the System drive also. This can be prevented by using a hidden file. More about that can be found here: Controlling Configuration Manager 2012 Using Hidden Files. But what to do when the Distribution Point is already placed on the wrong drive? Just follow steps in this blogpost for that.
Assuming that you're using ConfigMgr 2012 SP1, just download "System Center 2012 Configuration Manager Service Pack 1 Component Add-ons and Extensions". When installed open "Tools Command Prompt" and go into the ServerTools folder. Enter ContentLibraryTransfer.exe -SourceDrive <current drive letter> -TargetDrive <new drive letter>. For Example: ContentLibraryTransfer.exe -SourceDrive C -TargetDrive D
It will take a while (depending of the size on the Distribution Point) but the tool will do ALL for you. Just wait till it's ready and you're done. Much easier then with ConfigMgr 2007 a long time ago ;)
After copying data, SCCM services are stopped, DP shares are deleted, Permissions are set, WMI and Registry is updated, SCCM services are started again, old DP content is removed, and virtual directories are updated. All is done by the tool, so no worry about that. Quite cool that one single tool and command is doing ALL for you.
Hope it helps!