How to change page layout to portrait in LibreOffice 5 Impress

I cannot find any page formatting or layout controls in Impress (LibreOffice 5) I can’t change to portrait layout, I can’t change the page dimensions or any other page features. There is no “PAGE” under the FORMAT menu and there is no Page Setup or equivalent under the FILE menu. There is no page setup or layout options when I press F11 that brings up the Style and Formatting menu.

It is in menu Slide, item Slide Properties.

It is there. Many, may thanks. Although I am at a loss as to why any software engineer would bury something as critical as that so deep in the menus.