You should be able to upgrade (at a special "upgrade" pricing) to any of the VEGAS Pro 18 options, if your serial number qualifies. In the VEGAS Online Shop click "Information regarding the upgrade" and you'll see this text: "You can upgrade at a reduced price with a previous version or other authorized product. Please have your login details or serial number ready." You'll be informed if it does not qualify.

If you "upgrade", test with the free trial first "to check compatibility with your system and to avoid disappointment in case you dislike any new features or restrictions".

Please note that you do not have a "Sony Vegas".