Can I change my page orientation to portrait
Yes you can, it's not the conventional way where you just need to click a button. In storyline you need to change the height and width of the slide.
To change dimensions, click on the "Design" tab, then click on the "Story Size" icon (far left under the Articulate logo). You have to do is swap the two numbers in the dimension field. You will need to uncheck the "lock aspect ratio" button.
Here is a similar thread: https://community.articulate.com/discussions/articulate-storyline/how-to-set-page-orientation-to-portrait
Hope it helps. Please do not heaitate to reach back should you need assistance.
Wish you all the best.
Thank you, can you change it just for one slide or does it have to be the whole story
The dimensions apply to the entire file.