Well actually you did not meantion too much about your old Pro install as to how it is integrated etc. You merely meantioned how to switch to a different product vbGallery
So as you can see by my replies what you have to do depends greatly on your exact situation of which we do not have all the factors to answer you. Your old Photopost 4.7 could be a standalone not even integrated with vbulletin. Also as stated if you are already integrated with vb
upgrading your Pro to the latest will make the gallery work with the new vb4 series. You can import to the other product vbGallery if you want to do all the other work involved.