Why do it the hard way when it's so simple in File Explorer?
Anyway, open the Command form - Windows key plus R then type cmd into the Run box.
At the Command Prompt, start to navigate to your docx folder. Use the command
cd\ c:\users\{your username}\documents\sales
When you get there, type
ren sales\docx salesbackup.docx
hit the Enter key and you've finished..