You first choose a template for your resume when signing up for the resume builder. The template you choose will be applied in the resume builder the first time you log in.
You can always change the template applied to your resume by clicking on the "Templates" button on the left menu in the resume builder. Your written content will not change when you switch templates, but the flow of the content may be different (E.g.: content that used to fit on one page might flow onto a second page as each template has different dimensions/sizes/graphical elements).
Click on the Switch Templates option in the left menu to reveal the template options. You will notice your current document is selected.
You can scroll through the 16 different templates.
Note that some templates are available with the Basic (Free) and the rest will be part of the Premium plan.