In order to change the Basic Permissions in a Google Group, you must first access the MANAGE button:

Then, on the left-hand side of the page, you'll find Permissions > Basic Permissions:

Viewing

In the View Topics section, there are five customizable options for member management.  Simply click the drop-down menu to select your preference.

Note that "Example" was the name of the Group where this screenshot was taken.

Posting

In the Post section, there are four customizable options for member management. Simply click the drop-down menu to select your preference.

Always, Always, Always press the SAVE button when you make changes! 

Posted by K. Stesin'13 7/5/12