Depends on what you exactly mean:
-If you don't want page breaks to appear on the screen, select "View" --> "Web Layout". Page breaks do still exist, but you don't see them anymore.
-If you want to 'delete' all "manual page breaks" in a document (page breaks usually added by hitting "Ctrl+Enter"), replace "^12" with "" (empty string).
So, hit Ctrl+H, at "Find what" type ^12, leave "Replace with" empty, and then hit "Replace all".