I think you're misunderstanding "changing" here. It is being applied to the object of change, not the subject that is effecting the change. Whatever is changin

I think you're misunderstanding "changing" here. It is being applied to the object of change, not the subject that is effecting the change. Whatever is changing is being changed by another. God is not changing, therefore does not need to be changed by another. Immutability is one of the Divine Attributes (Aquinas talks about this as well).