Hi Rizwana,
As suman explained its a sensitive task.
Why you want to change NA to to Display attribute?
You want to effect (Navigational attribute behaves like Display attribute) it in any particular Infocube then just uncheck the check mark at cube level under navigational attribute column.
Or else you have to change object property at Info-object level but you need to take-care all the above suggestions.
Thanks
Aakash