Start by heading over to Website tab inside your portal.
Right away you'll see the different templates available to apply to your website. You have the option of previewing a template before committing to applying it to your website.
Hit Demo on the theme you'd like to view. It'll direct you to a preview of your website using that template.
When you decide on a theme that you'd like to keep, hit Activate, and you're all set!
If you decide later down the road that you'd like to switch it up, Bloom will carry over all of you're settings into the new template that you apply, no need to worry about losing any info or starting from scratch to set up your layout.