Need to change the product key that office 2013 was installed with?
Open a command prompt
And type the following (This is for 32bit office on 64 bit windows)
cscript “C:\Program Files (x86)\Microsoft Office\Office15\OSPP.VBS” /dstatus
Last 5 characters of installed product key: JHRTJ
cscript “C:\Program Files (x86)\Microsoft Office\Office15\OSPP.VBS” /unpkey:JHRTJ
Uninstalling product key for: Office 15, OfficeO365HomePremR_SubTrial5 edition
<Product key uninstall successful>
Next time you open up a office product it will ask for you a accounts or you can click to enter a CD key.