The owner of a user or usergroup can be changed either by DBAs who are owners of user definitions or by the system DBA using the Object / Change Owner function. This function is available in design mode.
In the resulting window, you can change the owner of the current user.
The system DBA is authorized to transfer not only his own users but also those of other DBAs to another user (also a DBA). DBAs can transfer only their own users to another DBA; for this reason, the Owner box for a DBA is preset to his or her own name and cannot be changed.