Windows does not allow to remap those keys so you will need third-party software to do this. AutoHotkey can do it easily.
Install AutoHotKey
Save following two lines as remap.ahk
(make sure it is not remap.ahk.txt
)
PgDn::Send ^#{Left}
PgUp::Send ^#{Right}
Now right-click the resulting file and select Run script
PageUp and PageDown should now switch desktops
However you will be unable to use a normal PageUp / PageDown function at all as long as the script is running
To stop it, expand notification area ("system tray") hidden icons area, locate a green square with white H
on it, right click and select Exit
For more info refer to AutoHotkey documentation.
You will need to run the script every time you log in. To start it automatically, right-click the script file and select Compile Script
. This should produce a new file with same name in the same folder as your script. Now press ⊞ Windows+R, type: shell:startup
and press Enter. A startup
folder should open. Place the new (compiled) file into this folder.
Thanks for accepting my answer. I added info on how to avoid clicking the script every time you start/restart your computer, if you need it. – Jack White – 2016-08-01T21:18:39.617