Delete manual page breaks one at a time or all at once, and fix the automatic breaks you can't delete.
On the Home tab, click the paragraph mark button (¶), or press Ctrl+Shift+8 on Windows or Cmd+8 on Mac. Manual page breaks now show as a dotted line labeled Page Break, so you can see exactly what you're deleting.
Click at the very start of the Page Break line and press Delete (or click just after it and press Backspace). The text below jumps up to fill the page.
Press Ctrl+H (on Mac, Edit menu, Find, Advanced Find and Replace). Type ^m in the Find what box, leave Replace with empty, and click Replace All to strip every manual page break from the document.
Breaks Word inserts at the end of a full page can't be deleted, but if a paragraph keeps jumping to a new page, select it, open the paragraph settings dialog, click Line and Page Breaks, and uncheck Page break before and Keep with next.
Click the ¶ button again to hide the marks, then scroll through the document to confirm the layout flows the way you want.