I needed to change a Windows Server 2012 installation from STANDARD to DATACENTER with KMS activation.
The process is still the same as always, but you need the keys. The can be found HERE.
The procedure:
To install a client setup key, open an administrative command prompt on the client,
type slmgr /ipk <setup key> and press ENTER.
If you need to activate it:
To install a client setup key, open an administrative command prompt on the client,
type slmgr /ato and press ENTER.
Windows 2012 and Windows 8 Client Setup Keys
| Operating system edition |
KMS Client Setup Key |
| Windows 8 Professional |
NG4HW-VH26C-733KW-K6F98-J8CK4 |
| Windows 8 Professional N |
XCVCF-2NXM9-723PB-MHCB7-2RYQQ |
| Windows 8 Enterprise |
32JNW-9KQ84-P47T8-D8GGY-CWCK7 |
| Windows 8 Enterprise N |
JMNMF-RHW7P-DMY6X-RF3DR-X2BQT |
| Windows Server 2012 Core |
BN3D2-R7TKB-3YPBD-8DRP2-27GG4 |
| Windows Server 2012 Core N |
8N2M2-HWPGY-7PGT9-HGDD8-GVGGY |
| Windows Server 2012 Core Single Language |
2WN2H-YGCQR-KFX6K-CD6TF-84YXQ |
| Windows Server 2012 Core Country Specific |
4K36P-JN4VD-GDC6V-KDT89-DYFKP |
| Windows Server 2012 Server Standard |
XC9B7-NBPP2-83J2H-RHMBY-92BT4 |
| Windows Server 2012 Standard Core |
XC9B7-NBPP2-83J2H-RHMBY-92BT4 |
| Windows Server 2012 MultiPoint Standard |
HM7DN-YVMH3-46JC3-XYTG7-CYQJJ |
| Windows Server 2012 MultiPoint Premium |
XNH6W-2V9GX-RGJ4K-Y8X6F-QGJ2G |
| Windows Server 2012 Datacenter |
48HP8-DN98B-MYWDG-T2DCC-8W83P |
| Windows Server 2012 Datacenter Core |
48HP8-DN98B-MYWDG-T2DCC-8W83P |
For reference, the legacy (older) keys
Windows 7 and Windows Server 2008 R2
| Operating system edition |
KMS Client Setup Key |
| Windows 7 Professional |
FJ82H-XT6CR-J8D7P-XQJJ2-GPDD4 |
| Windows 7 Professional N |
MRPKT-YTG23-K7D7T-X2JMM-QY7MG |
| Windows 7 Professional E |
W82YF-2Q76Y-63HXB-FGJG9-GF7QX |
| Windows 7 Enterprise |
33PXH-7Y6KF-2VJC9-XBBR8-HVTHH |
| Windows 7 Enterprise N |
YDRBP-3D83W-TY26F-D46B2-XCKRJ |
| Windows 7 Enterprise E |
C29WB-22CC8-VJ326-GHFJW-H9DH4 |
| Windows Server 2008 R2 Web |
6TPJF-RBVHG-WBW2R-86QPH-6RTM4 |
| Windows Server 2008 R2 HPC edition |
TT8MH-CG224-D3D7Q-498W2-9QCTX |
| Windows Server 2008 R2 Standard |
YC6KT-GKW9T-YTKYR-T4X34-R7VHC |
| Windows Server 2008 R2 Enterprise |
489J6-VHDMP-X63PK-3K798-CPX3Y |
| Windows Server 2008 R2 Datacenter |
74YFP-3QFB3-KQT8W-PMXWJ-7M648 |
| Windows Server 2008 R2 for Itanium-based Systems |
GT63C-RJFQ3-4GMB6-BRFB9-CB83V |
Windows Vista and Windows Server 2008
| Operating system edition |
KMS Client Setup Key |
| Windows Vista Business |
YFKBB-PQJJV-G996G-VWGXY-2V3X8 |
| Windows Vista Business N |
HMBQG-8H2RH-C77VX-27R82-VMQBT |
| Windows Vista Enterprise |
VKK3X-68KWM-X2YGT-QR4M6-4BWMV |
| Windows Vista Enterprise N |
VTC42-BM838-43QHV-84HX6-XJXKV |
| Windows Web Server 2008 |
WYR28-R7TFJ-3X2YQ-YCY4H-M249D |
| Windows Server 2008 Standard |
TM24T-X9RMF-VWXK6-X8JC9-BFGM2 |
| Windows Server 2008 Standard without Hyper-V |
W7VD6-7JFBR-RX26B-YKQ3Y-6FFFJ |
| Windows Server 2008 Enterprise |
YQGMW-MPWTJ-34KDK-48M3W-X4Q6V |
| Windows Server 2008 Enterprise without Hyper-V |
39BXF-X8Q23-P2WWT-38T2F-G3FPG |
| Windows Server 2008 HPC |
RCTX3-KWVHP-BR6TB-RB6DM-6X7HP |
| Windows Server 2008 Datacenter |
7M67G-PC374-GR742-YH8V4-TCBY3 |
| Windows Server 2008 Datacenter without Hyper-V |
22XQ2-VRXRG-P8D42-K34TD-G3QQC |
| Windows Server 2008 for Itanium-Based Systems |
4DWFP-JF3DJ-B7DTH-78FJB-PDRHK |