The command line is documented in the WSUS Operations Guide on page 65.
WSUS operation guide – Microsoft Download Center
Here is the process you would need to follow:
1. Create a folder called “content” on the new partition (e.g. E:content)
2. Then use the following command: %drive%Program FilesUpdate ServicesTools>
wsusutil movecontent E:content C:movecontent.log
This command will move the content folder from its current location to E:content and create a log file called movecontent.log on the root of your C: drive.