Depends,is it a IDI or DI(Powerstroke or not).If it's a PSD they are not hard but very time comsuming.You will have to pull the valve covers to gain access to them.If's a non PSD it is as easy as changing spark plugs sine they are on the outside of the head.Unless they have swelled they should come out easy.I've done a couple and always used Motorcraft's back.