I am talking about using Blogger own themes which can be seen on "Theme" page.
For example, at present you are using the "Simple" theme for your blog, and you would like to change or replace it with another Blogger's theme called Emporio.
The Blogger themes are: Contempo, Soho, Emporio, Notable, Simple, Dynamic Views, Picture Window, Awesome Inc, Water Mark, Ethereal and Travel
Note: This tutorial is Not about changing to a third party theme design.
Preview Blogger Theme With Your Blog
Before you decide to change into another Blogger theme, you can preview it first.
In other words, you can view how your blog look like with the new theme.
1. First you have to log into your Blogger account.
2. Next click on "Theme".
3. Then you scroll down and you can see the various Blogger themes showcasing there.
4. To preview it, select the theme you like to check it out, by clicking on the image.
5. It will show you how your blog looks like with the new theme.
6. To close it, click on the "X" sign on top right hand corner of the page.
Note: Don't worry. You still haven't made any change to your blog.
Change Or Replace Into Another Blogger Theme
Here is how you change to another Blogger own themes.
1. Log into Blogger account.
2. Click on "Theme".
3. Next click on the orange color "Customize" button.
4. Then you should see a page with the top part showing you the collection of Blogger own themes.
5. Now select any one from the Blogger themes.
6. You can view more choices by clicking on the white triangle symbol on the right side of the page.
7. When you click on a particular theme (Picture Window, Dynamic View, etc), it will show you more design from that theme.
8. Pick the one you like and click on the image.
9. Instantly you can see the preview right underneath of the page.
10. If you satisfied with the new replacement, then only you click on the orange color button "Apply to Blog".
11. Now you can see your blog using the new theme displaying on top left hand corner, with the caption below "Live on Blog, Based on Picture Window".
12. Then click "Back to Blogger" link on top right hand corner of the page.
13. That's all.