There is no current way to delete all Facebook Pages you've liked at once. But, if you are anything like me, at times your news feed starts filling up with posts from pages you've totally forgotten that you even liked. Maybe you liked it to help support a friend, or maybe you liked it because there was a contest going on, but now you want to clean up your feed. Here is the easiest way to do it…
Head to your Timeline and Click on ‘Likes.'
You will then land on the page shown below. This gives you a glimpse of some of your likes, by showing you the icons for the different pages.
From here you want to click the edit button to the top right hand of the page.
This will show all your pages organized by category and shown in icon format. In any of the categories just click on the pages icon, once you see the blue highlight around it you can just click delete on your keyboard to remove it. You can also hit the drop down to the right to see a list of all the pages liked in that category. From there you can go ahead and highlight each and hit delete. Once you have removed all the pages, from all of the categories you want removed, you can simply click the “Done Editing” button at the top. This will refresh your lists leaving only what's left.
You can also hit the button that says “Other pages you like” and it will bring up a pop up box (See below). From this box it's as easy as scrolling down the list and hitting the “unlike” button.