Importing older characters is simple and in many cases automatic. You can choose to do so by selecting the "Import" item in the File menu. Navigate to to the character file you wish to import to Vault of Darkness 2 and select it. VoD will do the rest for you.
Vault of Darkness is also smart enough to identify files you wish to open. If it sees a file that was created by a previous version of Vault of Darkness, it will automatically display a notification and ask for permission to continue to import the older character. If you click Yes, then VoD will import the character.
Please note, however, that when you save a character in VoD 2, the character may then only open correctly in VoD 2 -- not older versions of Vault of Darkness. Therefore, when sharing new or imported VoD 2 characters with your friends, be sure to inform them to open them with VoD 2 or newer!