If for some reasons, you decide to delete all published posts on your Facebook page, you can easily get it done provided you have admin access to the Page.
Just follow the steps below:
1. Go to your page
2. Click on "Settings"
3. Click on "Publishing Tools"
4. Tick the box next to "Posts" to select all
4. Click on Actions button, then click on Delete.
You can delete maximum of 25 posts at Once. So, repeat same process till you delete all your posts.
You can confirm if all posts have been deleted by checking your page's timeline.
I hope this works for you.
Check more Facebook page tips here.