Securing from unauthorized use - if you are connecting directly to your service provider the username and password they have supplied you should be sufficient to secure access. If you are using a router then you should password protect your router also. If using wireless access to a router then you should configure it with wap 2 password protection.
I'm afraid I don't understand this part of your post:
Is it possible to tune a connection as mine,and if it is,can you feel the difference.