How to Install Your Tumblr Theme Follow our step-by-step guide below to have your new theme up and running in minutes. Start by copying your new theme code from the page containing your purchased theme. Make sure you’re logged in to tumblr.com. Next, go to your blog and click Edit theme. Click Edit HTML, this will edit your current theme. Select your current theme code in the field and delete all of it. The field must be empty. Now paste your new theme code into the field. Click Update Preview. Now the fun part, click the Back Arrow to begin to customize your theme. Any customizations you make won’t show up on your live blog until you hit Save, feel free to play around. When you think it looks stunning, click Save. That’s it. Your new theme is now live on your Tumblr blog. If you’re having any difficulties after following the above steps, don’t worry. We’re here to help, contact us at firstname.lastname@example.org.