How change text case on Vivobook

I jus recently bought a new ASUS Vivobook laptop, and I find that I often hit Caps Lock by mistake, and end up with a string of upper case characters. I would like a way to select the all caps text and hit a key to change the case to all lower case, sentence case or maybe other combinations. Searching Google says that Shift F3 does what I want, but on my laptop this changes the screen brightness. One page said try Shift/Fn/F3, but this doesn't work for me either. On previous PCs I have just disabled the CaPs LOCK KEY, BU BEFORE i (see what I mean?) do this I'd like to find out if there is a change case technique that works on my laptop.

Thank you - Rowan