Boot from the USB/DVD that contains the Ubuntu installation files. As soon as your computer boots you should see the welcome window. Select your language from the list and click on Install Ubuntu.
Choose your keyboard layout and hit Continue.
On the next screen, select Minimal installation and check the box that says Download updates while installing Ubuntu and hit Continue.
The next screen will ask you to select your installation type, choose Erase disk and install Ubuntu and click on Install Now.
Note: You might get a different screen if pre-existing installations or other operating systems are detected from your hard drive.
A small window will pop up with an overview of the installation, review the details and click on Continue if everything looks correct.
If you are connected to the Internet, your location will be detected automatically. Check your location is correct and click Continue to proceed. If you're unsure of your time zone, type the name of a local town or city or use the map to select your location.
Enter your name, and your desired hostname for this machine. Next, enter a username and a strong password. You can also choose to enable automatic login by selecting Log in automatically.
The installer will now complete in the background. This should only take a few minutes, depending on the speed of your machine and Internet connection.
As soon as the installation is done, click on Restart Now.
After the restart, you should now see the login screen -- or the desktop, if you have enabled Automatic Login in Step 7.