This article only applies to the old designer. Not sure which designer you have? Check here.
Go to Design
From the merchant portal, choose Design from the navigation menu.
Go to the Designer
Find the section for Published Design and press the Designer button.
View Your Site on Various Devices
The Designer features a menu on the left side of the screen. At the top of the menu are icons for different devices (computer, tablet, and mobile phone). Simply press one of those icons to see how your site will look on that device.