The Steps to do are given here,
- Go to "My Computer" (Computer) , then right click the mouse at any blank space & select properties, here you can see the number of days remaining for the trial version.
- Make sure that only one day is left for end of trial version
- Then go to Start--> Right click on Command Prompt & select Run as administrator.
- Then the command prompt will show like this "C:\Windows\System32>"
- You just type this command to that "slmgr -rearm"
- like this "C:\Windows\System32>slmgr -rearm"
- After that, there will be a dialog saying Command completed successfully
- Now check the system. It will show the trial period remaining as 30days. Do this process whenever your trial gets over.