Upgrade Windows Server 2016 to 2025 in place

Microsoft's upgrade guidance says that from Windows Server 2025, servers that are not clustered can upgrade up to four versions at a time, which is why 2016 can go straight to 2025. Clusters using a cluster OS rolling upgrade can only move one version at a time.

If you are going to touch the server anyway, 2025 is the sensible target: it is the only one of the three still in mainstream support, and some vendors test only against releases in mainstream support. Pegasus says exactly that for Opera 3.

Microsoft lists restrictions for in-place upgrades of licensed Windows Server. The ones small businesses meet most often:

• Domain controllers need extra steps; Microsoft has separate guidance for upgrading them, and many administrators prefer to add a new domain controller and retire the old one.
• Server Core and Desktop Experience cannot be swapped during the upgrade.
• Language cannot be changed during the upgrade.
• Edition stays the same (Standard to Standard) unless you move up to Datacenter; you cannot move down.
• NIC Teaming has to be disabled before the upgrade.
• Evaluation copies cannot be upgraded to; install those clean.
• Hardware: Windows Server 2025 needs a 64-bit processor that supports SSE4.2 and POPCNT, among other instructions. Older hosts and some virtual machine settings fail this check.

Microsoft's guidance is blunt: unlike Windows client, each Windows Server upgrade requires a separate licence, and you need a valid product key and activation method for the target version. Your 2016 licence does not cover 2025 unless it had Software Assurance that included new versions.

Windows Server is licensed per core, and Remote Desktop users and devices need their own access licences. If the upgrade is also the moment you consider moving the server out of the office, compare the cost of buying licences outright with a hosted server where the Windows licence is part of the monthly price.

1. 01

   Inventory

   List every role, application, service account and scheduled task on the server, and who uses it.

2. 02

   Check vendor support

   Confirm Windows Server 2025 support with each application vendor, including any SQL Server version on the server.

3. 03

   Back up and test the restore

   Microsoft asks for a full backup of the operating system, apps and data, with a restore test to prove it works.

4. 04

   Record the current state

   Microsoft suggests capturing system information (for example with systeminfo) before you start.

5. 05

   Upgrade in a maintenance window

   From Windows Server 2016, use installation media and run Setup: Microsoft's Windows Update upgrade route to 2025 needs Windows Server 2019 or 2022 as the starting point. The server restarts several times.

6. 06

   Test with real users

   Before you call it done, have the people who use each application try their normal tasks.