Serifi (free) gives you 3 classic layouts:
- Classic Right Sidebar
- Classic Left Sidebar
- Centered (no sidebar)

For the pro version, you get the above plus an additional 7 blog layout styles:
- Alternating (pro)
- List (pro)
- Masonry (pro)
- Cards (pro)
- Gallery (pro)
- Gallery Wide (pro)
- Minimal (pro)

By default, Serifi is installed with the Classic Right Sidebar layout chosen.

- Go to Appearance > Customize > Layout Options
- Look for the Blog Layout setting and make your choice from the dropdown list.
- Click the Publish button.