windows.old can i delete it ?

My neighbour has just upgraded from 8.0 to 8.1, but is now getting a message saying that the windows.old folder is taking up alot of space.

I have searched and can find various answers, but none tell me what i need to know. They say it can be removed if you haven’t placed anything in the Windows directory that you need to retrieve. Well, of course my old documents were in there, BUT have they been copied to 8.1 now ??

I dont use Windows anymore (Ubuntu freak lol) and am a bit worried about them losing there documents etc... common sense would say to me that when uprading it would copy everything like that across to the new Windows 8.1 folder.

So, the question is has it ? and am i safe to delete the windows.old folder for them :confused:

p.s. its running 8.1 now and i am accessing their documents, so i am presuming they have been copied across, and its not accessing the ones inside 8.0 still.......

Any help would be very usefull please, thanks in advance