Help me unfriend

How do I permanently unfriend someone and make sure they don't blackmail you with what they know about you because they're dodgy that way. Currently my only plan is either delete all  people or wait till the drifting happens after uni starts and slowly delete them all. But then there's phone numbers and email addresses and my home address AND EVEN THIS BLOG fk Selena what have you done Duck WARNED you about this yet you thought you were SO SMART you could outsmart everyone look at you now I knew this would come back to you one way or another.