Here, a distinction has to be made between two cases:
1.) The document has not yet been activated: Yes, a replacement is still possible. You can upload a new file on Dissertation Online using the function
"Authors’ section" / "Additional Upload" ("Autorenbereich" / "Nachträglicher Upload").
2.) The dissertation has already been activated on our dissertations server: A replacement is only possible in justified cases (usually where legal matters are concerned). Here, the administrative effort is considerable.