Default owner permission needs to be modified in sharpeoint

Hello,

        I want to change Owner permission for whole site collections->sites in my whole Applications.

       So, I go to central Admin and went to web app ->permissions->owner and modify permissions.

       But not able to see in changes in sitecollection owner permissions as he is still able to edit page/ add webpart.

        Also i reset iis also.What can be done for that.Am i missing anything?

        Kindly revert.

       Thanks in advance

Varsha Patil