how I can change the direction of owa

1.  Open Exchange Management Console.
2.  Expand Server Configuration.
3. Click on Client Access.
4. Select the Outlook Web App tab below (it should be selected by default I believe.)
5. Right click and Select Properties on the corresponding OWA item or just double click on it.
6. Change the Internal and External URL as you want too.

Remember by doing this you will need to update your DNS records, both internal and external to point to the correct namespace.

Thanks

Here is a picture of when you are on the correct screen.  
Exchange-OWA-Pic.jpg

ok, ok but, I do not what do you mean about :

Remember by doing this you will need to update your DNS records, both internal and external to point to the correct namespace.

where I see it in my DNS?

this a good opinion