Via the payment method associated with your Microsoft account. More at https://www.microsoft.com/en-US/windows/extended-security-updates?r=1

How to get Windows 10 ESU

ESU is rolling out to eligible devices running Windows 10, version 22H2 prior to the end of support date on October 14, 2025, with availability expanding gradually as the phased rollout progresses. To get ESU on your Windows 10 device:

1. Go to Settings > Update & Security > Windows Update. If your device meets the prerequisites, you’ll see a link to enroll in ESU.
2. Once you select Enroll now you’ll start the ESU enrollment. If you are signed into Windows with a local account, you will be prompted to sign into your Microsoft account. If you are already backing up your PC Settings, you will see a prompt to enroll your device.
3. If you aren’t backing up your Windows settings, you can choose if you want to begin backing up your settings, redeem Rewards, or make a one-time purchase to enroll in ESU.

You can use your existing ESU license on up to 10 devices once you enroll in ESU. Just go to Settings > Update & Security > Windows Update and select Enroll now on those additional devices. If you are already signed into the device with the same Microsoft account used to enroll your first device, select Add device. If you are not signed into the device with a Microsoft account, you will be prompted to sign in to the Microsoft account used to enroll the first device.

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hth

Marcin