You can download latest version of Ubuntu from their server and then write it to your CD and then boot it and install it from there. But creating a booting CD is not a good idea if you are using Ubuntu as your secondary OS.
You can make a bootable USB drive and then boot from it to install it.
To make a bootable USB you need to have :-
- Windows Installed,
- Universal USB Installer, Download it from HERE,
- And a ISO Image of Ubuntu on your computer which you going to install,
- A USB with at least of 2 GB space and formatted with Fat system
Here we go :-
- Launch Universal USB Installer, it’s a portable app,
- Now first select the version of Ubuntu which you had and you are going to install, then Browse your ISO file and at last select the drive letter of your USB drive and the click on Create,
- Now it will extract files from ISO and put it in your USB,
- Now finally it will make your USB bootable,
- Now just boot your computer from USB to install it.
Don’t Forget To Make Your Computer Bootable Via USB, just enter your BIOS menu and tweak there.