Type in the custom height and width of your design.Tick the “Custom Dimensions” box on the drop-down menu.Click on the “Resize” option in the upper-left corner of your screen.Keep in mind that this feature is also only available to Canva Pro users. Since the one-click method is identical on both Mac and Windows 10, we will go through another useful technique you can use to change dimensions in Canva – the custom dimensions method. This allows you to make copies of your dimensions and paste them to different pages and projects. To go a step further, you can click on the “Copy and Resize” button, which is next to the “Resize” button on the drop-down menu.