Ah, I think I understand. When you choose a specific version, it uses an update file you have previously downloaded back when you had ESS. After running once, if you simply restart Spine then it will download the PRO update file. To prevent it from using any old ESS updates, you can delete all the files out of your Spine updates folder (or just delete the whole folder), here:
Windows: <user home folder>\Spine\updates\
Mac: <user home folder>/Library/Application Support/Spine/updates/
Linux: <user home folder>/.spine/updates/
