Tumblr is a blogging platform designed for people who have an interest in blogging, but not necessarily in HTML code. To help you customise your blog and express your personality, Tumblr offers a wide variety of standard free themes and premium paid themes, all of which are accessible from the site. Anyone can create a Tumblr theme and upload it for others to use, which can sometimes make it difficult to find a specific theme in the Theme Garden. If you see a theme on someone else's Tumblr that you want to use, you can use the credit link that is present in most themes on Tumblr.
Navigate to Tumblr.com, and log in to your account.
Locate the Tumblr user whose theme you want to get, and navigate to the user's tumblelog home page. From the Dashboard, you can click a user's avatar to go to his tumblelog.
Scroll to the very bottom of the page. If the person has enabled Tumblr's endless scrolling features, you will have to scroll to the last post.
Look for the theme credit link at the footer of the page. It should say "Theme by" or "Designed by." This varies between themes.
Click the credit link. This will either take you to the theme page in the Tumblr Theme Garden or the theme developer's page. Both provide the option to install.
Click the "Install" button just under the theme on the developer's site, or click the "Install Theme" button on the Tumblr theme gallery. Confirm you want to install the theme when prompted by Tumblr.