Hmmm.
Toshiba has not been very helpful in their documentation either.
I know some brands allow you to set how you want the Function keys to function in the BIOS, but I don't know if Toshiba is one of them.
If there is no option to change the behaviour in the BIOS, as you mention, then there must be a Toshiba utility (installed on your system currently, or downloadable) that you can use to change how it operates.