Hello there, Thanks for using Justanswer. I am Nimman and I will be assisting you .
What happens when you try to install ?
Do you get any error ?
It says system is not able to install. Is it because I am not running Windows 7 or8?
Are you using Vista ?
I am really sorry that you cannot use Word 2013 on Vista or XP.
You need Windows 7 or Windows 8 to run it.
how can I install Windows 7 or 8?
You need to purchase a Windows 7 or Windows 8.
Can I do so online?
Sure. You can buy online.
From the Microsoft store or any other websites like amazon etc.
Which site should I visit?
Above link is Windows 7
You can buy Windows 8 from this link CLICK HERE
Thank-you for your help
You are welcome.