If you are able to use Photopost Pro without purchasing another license you will see in your members area links to download that product, You can use either or but not both.
You can not upgrade to Photopost Pro. You must install Pro and import the vbGallery contents to Pro. They are different products but pro integrates with the front end look and feel of vbulletin as shown on many examples on our site.
Photopost vbGallery to Photopost Pro Import Script