Hi Ivan,
DBXL doesn't have a feature to allow renaming of document types at the moment. We will take an action item to investigate this option for a future release of the product.
One possibility might be to use the Save As option for a document type, which effectively saves the same document type configuration but with a new name. However, you'll still have to export the xml documents from your source document type and import them into the new document type. You can migrate documents using the Migration Tool, or using the export/import options in the Documents tab. If you need additional guidance on either of these please let us know.
Thank you.