From FezWiki

There are 2 ways to change the document type of an existing record -

• Clone an existing document -
  • Click the More Options icon against the appropriate record in Browse or View Record mode
  • Click the Clone Selected Record link
  • Select the appropriate Destination Collection etc in the Clone Selected Record form
  • Click the Clone Record button
  • Edit the new record as required. Be aware that there may be some loss of data if there are discrepancies between the old and new XSD displays
  • Click the Submit for Approval or Publish button as appropriate.
  • Delete the original record/object if necessary.

• Change the xsdis_id in fedoraAdmin -
  • Access the FezMD datastream of the record you wish to change
  • Change the xdis_id value to the value of the new document type. Ensure you use the FOXML xdis_id for the appropriate document type, not the MODS or DC xdis_id.
  • In Fez, reindex the object.