The email actually was not an invite to convert from photopost pro to vbgallery. It states there is the ability to import vbulletin albums into vbgallery.
You can convert from pro if you wish but you would need to use the pro to vbgallery import script in the import forums. the importalbums.php script in the new vbgallery is for the vb albums import.
You will have full access once your renewal is processed and you can decide which way to go.