How to move position of page numbers?

I guess someone else set up the document for you or you are using a template. The page numbers are on a parent page. In the Pages panel at the top you will see all the parent pages for the documnet. Go there to edit objects and text on parent pages. Changes made there will appear on all pages that use that parent page.

You can also override individual instances of parent objects. Hold Command+Shift or Control+Shift as you click on an object while on a normal page. You will promote the parent object to be a normal object on the page you are editing. Now you can move, edit, or delete the object. This will not otherwise affect the parent page or any other pages in your document.