How to Delete People That Are Following You on Twitterby Tammy Columbo
Though you can’t force a user to unfollow you on Twitter, you can delete the follower from your Followers list by blocking his account. The user is not notified when you block him, but your tweets no longer show up in his searches or timeline. However, your public timeline is visible to everyone, including blocked users. To remove someone from your Following list without blocking him, just unfollow the user.
Open the user's profile page, and then click the arrow next to the gear icon in the toolbar at the top of her tweets. Click the "Block" option to block the user, or click "Block and Report" to block the account and send a notification to Twitter support. The button label changes to “Blocked.”
Open the user’s profile page, and then hover over the "Following" button; the label changes to “Unfollow" and the color of the button changes to red. Click the button to unfollow the user; the button label changes to “Follow.”