1. Format->Styles and Formatting
2. Click the Page styles
3. Right click and select “New”, this will start creating a new style
4. Name it “Portrait” or whatever name you need
5. Click on the page tab and choose the orientation to be “Portrait”
6. Do the above steps again for a style that you name “Landscape”, although it should be there by default, but if you don’t find it, just create it
7. Whenever you need to switch the page orientation, click Insert->Manual Break->Page break, and choose the style you want to apply to the new page

Voila! There you go 🙂