Email problem

Since Apple updated software, every time I want to buy something or fill in a form that I’ve received in an email I get a narrow strip with the information I need to fill in appear on the right side of the screen which I find difficult to fill in and also to see. Why do Apple repair something that’s not broken? Is there any way that I can change it back to how it used to be ie full screen? I’m seriously thinking of changing to a samsung