Never looked a a focus one, so would not like to say, but if same as mondy, then switch on passenger side should just prise out.
If you have rear electric windows you could always try one of those switches to make sure it is the switch.
If you can get it open by prising just use some old knackered emery cloth to clean contacts then coat with coppaslip afterwards.
DO NOT UNDER ANY CIRCUMSTANCES USE GLASS PAPER to clean the contacts.
tabetha