Group Assignements

I think I have a simple and easy-to-answer question. My business case is that I have several blog entries which should only be accessible (read/write) for certain logged in users by group names.

– First, I installed “User Access Manager” and created two groups (“Group 1” and “Group 2”).
– Then I assigned “User A” to be in “Group 1” and “User B” to be in “Group 2”
– Then one blog entry is assigned to “Group 1” and another to “Group 2”

Problems:

– I am unable to change the group assignments for the users
– Both users are in both groups

What didn’t I understand in setting up?

Thanks
Andy