Renault Clio 1.2 16v. How can i fix heater fan?

I have a 52 plate Renault Clio (non air-con) and the fan has stopped working on setting 1,2&3 but works fine on setting 4.Can anyone shed some light on what the problem could be? as i don't really want to take it to a garage and pay their huge labour costs for a problem which might be simple enough to do by myself. many thanks in advance.