How to delete Windows.old folder (tip)
1. First make sure that your latest Windows is working well. You have all the files, folders and software from old operating system running well inside Windows 8. Because once you delete this folder; you won't be able to retrieve your old Windows files easily. There are ways; but why not just spend a few minutes that everything's in place in the new environment?
2. Notice that your regular SHIFT+Delete won't work in case of the windows.old folder - because it's a system folder. You'll have to tell Windows 8 to delete your old Windows. For this, go to the step #3.
3. Open the Run Box (type Windows Key + R on your keyboard). In the run box, type following command -
cleanmgr
4. The cleanmgr command actually opens Windows inbuilt 'Disk Clean Utility'. You can rely on this utility as it's developed by Microsoft and can be used safely without worrying about deletion of any important or operating system critical files.
5. Check the partition (aka drive) on which you've installed your Windows 8. In 99.99% of the cases, it will be your regular C:. Select the 'C:' from the Disk Clean Utility as the drive you wish to clean.
6. On the next screen that will appear on the utility, select 'Clean Up System Files'. Don't worry - this is a safe option and in the next step, you will get all the options to select the files that you want to remove from your system.
7. Let the cleanup utility perform a quick scan of your machine. It will now show a new option in the list "Previous Windows installation". The size of windows.old will be ~10 Gb depending upon your previous setup. But that's a pretty large disk space you can clear with this tool.
8. Hit 'Ok' button and wait until the utility performs a safe cleanup of your C: drive. It will preserve all the important files in the current operating system and will only remove the old windows installation files.
Additional Tip: You may choose other options present in the list and it's completely safe to use it.
If you have questions or issues with these steps, feel free to ask them below. We've several Windows experts here who'd be willing to help you.