I had on my to do list to write a detailed post on how to remove the Windows.Old folder after upgrading. While reading through some Rick Claus I noticed he already had a great post on it. Thanks Rick, you saved me a bit of work. You can find the Step-By-Step on his blog at How To: Delete Windows.Old from an upgraded Windows 10 / Threshold system. These instructions use the Download Junction.EXE from Sysinternals to do the heavy lifting. The identical instructions should work for prior versions of Windows Client or Window Server as well (back to 2000). In a future post, I may opt to build on it with PowerShell and just give you one quick script to do it all. But for now. Task complete!!!
See Microsoft KB article for tips on using junctions.