You can pry the piton out with alternating blows from the sides, after which the piton will gradually inch its way out. Using the pick of a mountaineering hammer the piton can be pried out in an upright fashion from the rock crack. Be careful of rough pulls on the piton, which could cause it to fall and you would lose it. There is also the option of using a so-called piton retriever. (Video from e-book Mountaineering Methodology, www.mountaineeringmethodology.com)
