How to Extend Evaluation License

Objective: To extend the windows server evaluation license for extended use after 180 days

The evaluation versions of Windows Server are valid for 180 days by default and can be extended.

To extend the evaluation period the following steps can be used:

STEP 1. Open an elevated command prompt (cmd)
STEP 2. Enter the following command:

cscript.exe %windir%\system32\slmgr.vbs /dlv

The Windows Server evaluation version can be used for 3 years.

To rearm use the following command:

STEP 1. Open an elevated command prompt (cmd)
STEP 2. Enter the following command:

cscript.exe %windir%\system32\slmgr.vbs /rearm

Restart the system
After the restart the evaluation period is extended for another 180 days

Source of information