You can upgrade to PGP Encryption Server 10.5 by doing a fresh install from *.iso and restoring a backup from PGP Encryption Server 3.3.2 or above.
When you upgrade in this way, and you have customization scripts, you will need to take this into account.
PGP Encryption Server 10.5
This will only potentially cause a problem if you had made customizations to any of the pgp*.sh scripts in the /var/lib/ovid/customization directory in your previous release.
Customizations are to be approved by Symantec Engineering only. If you have custom scripts, we recommend reaching out to Symantec Encryption Support to review if these customizations are still needed post upgrade. In most cases they will not be.