1. Getting started
Before you begin, you need to download Ubuntu and, if you want, verify the download.
Once you’ve done so, you can create your installation DVD. The procedure may differ slightly depending on which version of Ubuntu you are currently using.
2. Burn a DVD
Insert a blank CD into your burner. A ‘CD/DVD Creator’, ‘Choose Disc Type’ or ‘Blank Disc’ window might pop up. Close this, because we will not be using it.
3. Install Brasero
16.04 LTS no longer comes with a CD/DVD burner, so using the Ubuntu Software Store, search for ‘Brasero’ and click ‘Install’.
4. Start Brasero
Open Brasero and click on the ‘Burn image’ button.
Then select the ISO you downloaded in the ‘Select a disc image to write’ box and your DVD drive in the ‘Select a disc to write to’ box and click the ‘Burn’ button.
5. Burn a DVD with Brasero
Once the DVD is burned, you can restart your computer and try or install Ubuntu.
6. Next steps and finding help
If you want to install Ubuntu, try the Install Ubuntu desktop tutorial
If you get stuck, help is always at hand.
source : https://ubuntu.com