Deleting windows previous installation files and windows.old files

When you try deleting files of previous windows installations without formatting the drive you get errors like admin rights required. Even if you are the admin it doesn't allow you to delete some of the files.
Its easy to delete those files with just the tools given in windows and there is no need of other 3rd party tools.
Follow these steps to delete previous windows installation files

1.Right click on the drive in which the previous windows files are present.
2.Then select properties.
3.In properties select disk cleanup option.
4.Then select Clean up system files.
5.Then it will calculate and show you all the unnecessary files.
6.Now after completing all the steps and deleting you can find that those files are deleted.