Design sets can be found in your settings. Select 'account' and 'settings from the top right, then select 'design lab' from the left menu, then select 'design sets'.
Here we have a large range of design sets to suit all styles. Once you have your colours and fonts chosen, click through the design sets to find on that suits you.
You'll see the template previews on the right, click through the small thumbnail images to preview each template.
Tip: Colours work differently on different design sets, so if you've found a design set you love but your colours aren't quite looking right, don't worry. You probably just need to switch them around a little by going back in to the colours section.
Once done, don't forget to save all your changes.