What options do I have to refinish the exterior of my house?

I have a cape style house with stained cedar shingles. The stain is starting to lighten up and looks as though it needs to be refinished. Is it possible to restain the shingles? How often do the shingles need to be replaced? I bought the house a year ago and the previous owner had new shingles and stain done about 6 years ago.