Sign into Blogger DashboardScroll Down and Click ThemesThis will open the list of themes. Select a new theme by clicking on it. When you've selected the "Just Right Look" click the orange apply to blog button.
In the Docs Toolbar click file followed by scrolling down the list and selecting "See Revision History".
When viewing revision history if you click the arrows it will refine the history into smaller chunks of time.
Best, Ms. Drasby