How can I change the displayed fields of a lookup value?

How can I change the displayed fields of a lookup value?


When a lookup field is created, we need to select a display field. When I edit the lookup field properties I cannot change that field. I tried to change it in the script but received:

Error modifying the page
Error at line : 43
Type change from import type to another import type is not allowed as it may lead to data loss.If data is not a problem, then kindly delete the old import field and add the new one on your own.

How can I change the display field in a lookup field?

Thank you
-andrzej