How to get Windows 10 Long Term Service Branch (LTSB)?

Windows 10 Enterprise LTSB is only intended for purpose-fit machines (e.g. POS terminals, ATMs, digital signage, medical devices, etc.) and should not be used on consumer machines. Consequently, it is not available through traditional retail channels. If you're looking to upgrade, Windows 10 Home or Pro is likely what you're looking for.

However, a 90 day free trial for LTSB is available for download on TechNet. You'll need to log in with a Microsoft account and register specifically for evaluation. Use beyond the trial period will require a volume license agreement with Microsoft.

LTSB is available only in the Windows 10 Enterprise LTSB edition. This build of Windows doesn’t contain many in-box applications, such as Microsoft Edge, Windows Store client, Cortana (limited search capabilities remain available), Microsoft Mail, Calendar, OneNote, Weather, News, Sports, Money, Photos, Camera, Music, and Clock. Therefore, it’s important to remember that Microsoft has positioned the LTSB model primarily for specialized devices.

Microsoft never publishes feature updates through Windows Update on devices that run Windows 10 Enterprise LTSB. Instead, it typically offers new LTSB releases every 2–3 years, and organizations can choose to install them as in-place upgrades or even skip releases over a 10-year life cycle.

If you want to use LTSB, you need to pay for it, but you could register a Microsoft account to download an 90 days Evaluation version, only on trial.

https://www.microsoft.com/en-in/evalcenter/evaluate-windows-10-enterprise