After Updating Windows 10, How To Delete Windows.old (Previous Windows)

Hello friend!How are you? Hope you are very well. I used genuine windows 7 home premium 64bit operating system. Last 29 July 2015 Microsoft has released windows 10 and they announced every genuine operating system can be upgraded to windows 10. So that I have wanted to use genuine windows 10 and wanted to update my windows 7 to windows 10.After updating windows 7 to windows 10 I was so happy but