How to delete windows.old in Windows 7

When we upgrade Windows 7 from a 32 bit version to 64 bit version, there is a folder called Windows.old get created the drive which may take up  a huge disk space. Here is how we can get rid of that:

• Click on Start -->All Programs-->Accessories-->System Tools-->Disc Cleanup.
• When the dialog box comes up, select the drive that has the .old files on it and  click OK.
• The system then scans for the files to be cleaned up and another dialog box opens with the selection.  Click on the button labeled Clean up system files at the bottom of that dialog box.
• Another dialog box will come up, select the drive again that has the .old files on it.  The system will perform another scan for the system files that need to be cleaned up.
• After scanning, another dialog box opens up and there you will find a list of check boxes.  Scroll through and check on the box labeled Older versions of Windows and click OK.
  

This can also help:

Click Start-->All Programs-->Accessories-->right-click "Command Prompt", and then click Run as administrator. Run following 3 commands on command prompt

takeown /F c:\Windows.old\* /R /A

cacls c:\Windows.old\*.* /T /grant administrators:F

rmdir /S /Q c:\Windows.old\