My son has Windows 8.1 on his notebook with Microsoft Office 2013 trial which has now passed the trail period expiry date.

I have purchased Office 365 and would like to install it on his notebook.

Do I need to uninstall the trial copy on his notebook or will the installation recognise it and deal with it accordingly?

Hi,

If it was a trial of Office365, you can "convert" the trial to a licensed copy.
If it was a trial of Office2013, you should uninstall that, then install Office365.

(although they may appear to be the same, Office2013 is different from Office365, the licensing control mechanisms are different)

Please visit the appropriate Microsoft Community Office Forum for assistance.  Thankl you!