Im getting rid of a computer and i need to clean it of my internet activity. Obviusly i deleted the browsing history but what else?

Like when i go to the URL and i type...www.D and then a drop down menu comes up and it gives the names of all the sites i have been to that start with the letter D like Dreamviews. How can i stop it from doing that? And when i go to youtube and i type in something like the number 2 a drop down menu comes up with lets say 2 girls 1 cup. How do i stop the computer from doing this?