My b2evolution Version: Not Entered

Hi, thanks again for your help!
I have another questions. I've created 3 blogs, included the ogin true code so that everyone needs to login. I've played around with settings so that basic users can only comment and not post content.
Now, I need to give access to 2 of the 3 blogs to some users, and give access only to the third blog to some others...
What is the easiest wy to do it?
Thanks!!