Package Export & Import

Hi Eli, I want to update an item, e.g. a list or a form. If I use the merge option during import, the list is not replaced, instead it has old values which was dropped from the list to be imported. And similarly for form, fields are merged instead of being replaced by the form exported. So far I have not been able to import successfully without errors, especially when an item type has relationships. Can you advise the exact steps & options required to do a successful export and import?