In Windows, go to Settings and then click the “Apps” icon.
Scroll down until you find the entry for PMDG. It should say something like “DC-6 Base Package.” Click on that entry and the option to uninstall will come up.
Reinstall using the original installer you received when you purchased the DC-6. You’ll have to re-enter your license key.
Note: above instructions are for purchases made for the PC, via the PMDG website.