When the Windows 10 documentation was being updated, Microsoft revealed that starting with version 1903, May 2019 Update, the storage requirement will increase to 32GB or greater for the 32-bit and 64-bit version. However, a new documentation page (via Neowin) clarifies that the new minimum requirement is for manufacturers building new computers only, and it doesn’t apply to devices already running Windows 10.
So, if you have a laptop or tablet with limited storage already running a version of Windows 10, you’ll be able to upgrade to the May 2019 Update and continue to receive updates.
The reason why the company is increasing the storage requirement for PC manufacturers is because starting with version 1903, Windows 10 introduces “Reserved storage,” a new feature that reserves part of the available storage (around 7GB) to reduce issues during the upgrade process, and it’s a feature that enables automatically during a clean install.
