wifi cannot be switched on or off, any help?

The switch/option to turn the wifi on and off freezes, ie it's blanked out, so I cannot turn the wifi off (or on if it's already off). It does work for a while but then it stops responding and blanks out.

This has only developed recently, it used to work fine. I don't think I've added any apps to affect this. I have to turn the phone off and on again to change it

I haven't upgraded my adroid yet - don't think i have - as i don't see a way to do it - the web page doesn't give an option to upgrade. only says there's one available...

Any advice or  help would be very welcome indeed!