1. Login to your WordPress admin dashboard.
2. Under the dashboard menu, hover your mouse on "Appearance"? and then click on "Themes".
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3. Click on "Add New"?.
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4. In Add themes page, you can search for a theme or browse the themes from "Featured"?, "Popular"?, "Latest"? options. If you hover your mouse over any themes, you will be presented with two options - "Activate"? and "Live Preview"?.
5. Hover your mouse on any theme you like and then click on "Install"?.
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6. A newly installed theme will show you the "Activate"? option. Click it!
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Congratulations, you have installed and activated a new theme on your blog.