How update value fields of all old post?

Hi we have a problem with the ACF plugin.
If we create a text field and give it a default value, but later update this default value, in posts where it has already been entered the old value remains, instead in new posts the new value is entered.

To standardize the new value across all posts we are forced to delete the field and create a new field with a different name.
If we delete the field, and recreate it with the same name and different value on the new posts I have the new value, instead on the old posts the old value reappears.