How do you change a photo (and it s contents) from portrait to landscape?

You know how to rotate. You gave an example of what happens when you rotate. What exactly is the problem? Are you wanting to convert the image from portrait to landscape with all the elements inside still correctly oriented? Like this below? You'll have to cut, paste, rearrange, recompose, and redraw each element whatever is necessary.

For Photoshop or any program that allows "layers"

Open a new file that is in landscape mode that is the same size or bigger than your base photo (your advertisement) Open your base file. highlight 1/2 of your base photo, say the burger. Copy. in your new file paste the burger into a new layer and rotate that layer. Do the same thing for your text or anything else and cut and paste into another new layer. Each layer can be manipulated until the layout is what you want Don't forget to save your new file all along the way. You can then "flatten" the file and "Save As" under a new name and as a JPG if that is what you need.

What you showed is exactly what rotating does. To convert a photo from portrait to landscape, you have to crop that portion that you want to be landscape. You cannot capture the entire photo. Irfanview is a nice free program that lets you crop and resize easily.