How to enable the disabled fields in crudformfactory

I have made some fields disabled by using this code

 crud.getCrudFormFactory().setVisibleProperties(UPDATE, "firstName", "lastName","username","role");

how to enable it.

Sorry, trying to understand the context here: Is this for the add-on Crud UI Add-on - Vaadin Add-on Directory by @alejandro.du ?

yes it is for that only.I want to enable that field immediately if i choose a particular value from comboboxProvider
Code explained here
How to add new field in CrudFormFactory based on some field value.Please Help