From the software
After you've updated your design, open the menu in the editor then click Share in the upper right corner.
A needs sync message will appear as shown below. Click needs sync, then click sync changes. It's as simple as that!
From your homepage
From Home or All My Designs, hover over the design you would like to sync changes from. Click the three dots as shown below. Tools will appear including Share. Click needs sync, then sync changes.