C:\Program Files\Microsoft Office\Office15\OSPPREARM.exe

Run it and earn more days...  :) 


PS: it works only 5 times, it means 5*30 days. (Rearming the Office 2013 installation) 

Rearming does the following important tasks:
 - Resets the grace timer to 30 days.
 - Freezes the grace timer until either an Office application is run, or the ospp.vbs script is run.
 - Resets the client computer ID (CMID). This is important because the KMS host uses the CMID to determine the number of unique clients. To check the CMID, use the command ospp.vbs /dcmid.