On an HP Spectre x360, the F-keys are by default in the "Fn"-state, where they do fairly handy things like turn up/down volume or brightness. But F11-for-fullscreen and F2-for-renaming are really handy – is it possible to switch Fn-state for only certain keys? (I know I can switch for all keys in BIOS, but I'd like to keep the best of both states …).
(I'm using XFCE/Xubuntu.)
Go to the cog wheel in the upper right hand corner of your screen and select "System Settings"
Select "Keyboard"
Go to the "Shortcuts" tab
Select "Windows" in the left panel
Find "Toggle Full Screen Mode"
When you do this it will wait for you to push your short cut ex.. Ctrl+F11 keys or just simply push the F11 key
To cancel push the Backspace key.
Taken from the url below
https://help.ubuntu.com/stable/ubuntu-help/keyboard-shortcuts-set.html