Hi.

When I run Windows update, there is a link in the left hand margin that prompts me to install additional features to Windows 8.1.  I have no idea what additional features are available, but I would like to have a look.

Only trouble is, when I click on the link, I am prompted either to buy a product code or to input a product code that I already have.  Presumably I do already have one - as I am running a paid-for version of Windows 8.1 pro that came pre-installed with the machine.  But I cannot find any product code in the documentation supplied with the machine.  Where do I go for this, please?