Things below are just an alternative. There is an official way to do this.
Get a USB stick
Make sure you have an usb stick with enough storage. Mine is 8 GB.
Format the USB Stick
There are plenty options to do this. My solution is using the built in one
disks
- Click the USB device
- Click the square button
- Select EXT4 as the type of parition
- Done
Download Ubuntu ISO
Bootable USB
- Install and Use UnetBootin
sudo apt-get install unetbootin
- Launch UnetBootin
- Select the Ubuntu ISO
- Select your USB drive
- OK
- Done
Now, you have a Bootable USB for ubuntu :D