In order to export your Performance Page data, you will have to:

- Make sure you are on the right social profile, it should be your Facebook Page highlighted on the top right corner 

- Click on the left-hand side menu

- Go to Analytics

- Go to Page Performace

- Each of the Features has a grey arrow on the top right of their window frame

- Click on the format of your choice 

You will find here the formats available. If you rather export them as a graph then you can have a look at this article.