When I'm trying to boot to BIOS on my ideapad S210, it simply go directly to Windows 10. It's something to do with the "shutdown" mode of Windows 10, which is not really a normal shutdown, but like a sleep mode.
To solve it:
1) Restart Windows 10. (Again, a shutdown in Windows 10 is hibernation)
2) Press F2 (or, FN+F2 if you have a keyboard with function keys in orange text). Besides, if you just want to change the startup boot device, it's F12.
Now your ideapad should be able to boot to BIOS.