You don’t need to delete your articles. You can just import the Sports dummy content without deleting any content of Fashion.
And you can also change the structure without importing the demo because demos are also the same theme with different variations of settings. So if you want to change the setting regarding the banner section then please go to ‘Appearance > Customize > Banner’ then you can play with the respective setting for different structural preview. Like you can change the layout by hiding some section which you don’t want to show.