How to find and delete large files on a PC

A friend of mine has written to me:

I keep getting message ‘delete some files’ as there’s a memory [disk space] problem with my laptop. Which files would you delete?

I would delete the biggest files first! Don’t delete anything in your Windows directory though, or Windows might stop working.
You can bring up Windows Explorer and sort by file size.
I’d look in your downloads folder first. Any video is likely to be large. Sounds files can also be quite large.
There are free utilities that can search your whole disk and show you the biggest files. Have a look here, and probably start by downloading the first one, Treesize Free: