Not sure how it is done manualy.
I used to get the same problem with callers being directed to my answer phone.
I phoned my provider up and told them that I did not want any more answer phone messages and they cancelled it for me.
Now my phone rings till I either answer it or the caller gets fed up and stops ringing.
i am sure there must be an easy way of adjusting it if you still want to keep your answer phone messages.
If you still have the booklet that you got with the phone it should tell you how to do it on that.