My b2evolution Version: Not Entered

I want to divide our blogs into section and list all the recent post ex:
Group 1 would list all the post that is recently posted in 1.1 and 1.2.
Group 2 would list all the post that is recently posted in 2.1, 2.2, 2.3.
Is that possible?

My website is about cars
Group 1 List (Cars)
1.1 New Cars - Category would be the car brand ex Nissan, Toyota
1.2 Old Cars
Group 2 List (Buy)
2.1 Dealship
2.2 Resale
2.3 Trade
Group 3 List (Repair)
3.1 Part Store
3.2 Tools and Tips

How do you change your default blog so that another blog become the default blog?