where are the abs sensors on my car?

i have a ford fiesta zetec(alloy wheels) the abs light has come on, i have been told to clean the sensors, where are the abs sensors situated on the wheel and the hub and what is best to clean the sensors with? will this cure the abs warning light fault or does anyone else know why the light could be on? also if cleaning the sensors does cure the problem will the abs warning light go off or will i need the engine managment system reset?