How to change object type

Documentum allows creation of custom types, which defines custom attributes in addition to the inherited ones. Once your custom type is defined and created in the repository, you can create objects - which are instances of that custom type.
If you have created objects of a certain (sub) type, you can still change their type. The easiest way is to use the following DQL:
CHANGE current_type [(ALL)] objects to new_type [update_list] [WHERE qualification]
* ALL - change type of all object versions
* update list - list of updates on objects attributes to perform during change type operation

Obviously current_type must be the supertype or subtype of the new_type. Thus, you can move the object instances through the types hierarchy up and down.
Ok, if you move from a supertype to subtype you get additional attributes that are empty. But what happens when moving from subtype to supertype? The custom attributes' values of the subtype are lost (you can use the update list if you want to copy the values to other attributes, that are not lost).

You should take note of the following constraints on this operation:
1. You can only change the type of objects that are subtypes of dm_sysobject. (If you want to change the object type of not a dm_sysobject, follow the procedure described here: URL).
2. The object's current type and the new type must have the same type identifier (which is the first two characters of the object ID. For example, dm_document has 09).
3. The old and new types can't be at the same level in the type hierarchy. The new type must be a supertype or subtype of the current type.
For example, you have a my_car and its subtypes my_toyota and my_lexus. In order to change an object of my_toyota to type my_lexus, you must do it in 2 steps:
change objects my_ford to my_car;
go;
change objects my_car to my_lexus;
go;

4. You must have DELETE permission on the objects you are changing.