All the Shopify themes (free and paid) are now up-to-date with Shopify 2.0 requirements. But you can still check for the same using the following steps:
From your Shopify store admin dashboard, go to Online Store > Themes
Find the theme you want to update and click on the version notification to see if an update is available
Next, click Add to theme library - this will make a copy of your original theme, download the updated theme version
Apply customizations using the theme editor