The Laserfiche Migration Utility can do this, but you'd have to be coming from Laserfiche 6 or 7 and going to a later version. If the customer is already on Laserfiche 8 and higher, then there's no direct conversion path to go from SQL Express to Oracle. An alternative would be to export volumes and attach them to a newly created repository using an Oracle backend, however you'd have to reconfigure security amongst other things.

As for general steps you can take outside of what Laserfiche provides, see this page.