Microsoft has provided Windows 8.1 and Windows Server 2012 R2 to test for evaluation. For Windows 8.1 you get a 90 day evaluation and for Windows Server 2012 R2 you get a 180 day evaluation. But what if you want to keep testing your software beyond those limits? Well there is a way to extend your trial!
The following are the steps in order to extend your Evaluation trial.
1) Open up a elevated command prompt
2) Type in the following command in the command prompt
3) A Window will Pop Up telling you that the command was a success
4) Reboot your OS and your evaluation trial should be extended another 90/180 days depending on the OS you are Trialing.
Please note that you can only do this 3 times.