Direct answer
Download the demo only from its official Steam page. Official news says the updated version includes Act 0 and Act 1 content for Groveshire and Gavault, additional Knights and secrets, the rewind mechanic, and six languages.
What the updated demo includes
The official update introduced the prelude explaining how the Sovereign came to be, two Act 1 main-quest threads, new playable Knights, secrets, and the Demon-linked rewind system.
Languages
Official demo news lists English, French, Simplified Chinese, German, Korean, and Japanese. Always check the live Steam panel before downloading if a specific localization is essential.
Save transfer status
The official materials collected for this guide do not clearly promise that demo saves transfer to the full release. Begin the full game expecting that a fresh save may be required unless the current store page states otherwise.
Frequently asked questions
Where can I download the Sovereign Tower demo?
Use the separate official Sovereign Tower Demo page on Steam.
Does the demo save carry into the full game?
The official sources used for this page do not confirm save transfer, so this guide does not promise it.