Select Assignments.
Select Assignments from the site's Tool Menu.
Select Permissions.
Select Permissions from the Actions Menu.
Modify the permissions for the roles listed.
Check the box next to each permission to allow for a given role. (Unchecking a box will remove the corresponding permission.)
Note: You may see different roles listed depending on the roles which exist in your site. A role must be present in the site in order for you to modify its permissions.
Select Save.
Select Save to save changes.