How to Change Themes

You can get creative with Blogger by choosing a unique theme. This is how to do so: 

1. Sign in to Blogger.
   

   
2. In the top left, click the Down arrow .
   

   
3. Click a blog to update.
4. In the left menu, click Theme. 
   
5. Click the theme you want to use. 
   
6. In the bottom right, click Apply to Blog. 
   
7. Optional: To save a copy of your theme, in the top right, click Backup/Restore  Download theme. 
   

Reference Link: https://support.google.com/blogger/answer/1227173?hl=en&ref_topic=6321969