How do you unfollow someone on Twitter?

go to the person's profile. you'll notice a shaded area at the top, with 'following' written on its left side.

in the same bar, on the right hand side, you'll notice two buttons. Click on the second one, that is, the one that kinda looks like the shape of the sun. The option for unfollowing is visible. There you go :)

PS - yeah, it can work on any Web Browsers like chrome, firefox et al

hope this helped :);)