corsa 1.7dti low blow egr valve how to remove it and clean it?

hi my brother in law has just bought a 52 reg corsa 1.7 dti low blow which i believe is about 68 bhp. for some reason this has a lack of power which i have been told it is the egr valve being the fault and this can be cleaned. any information on how to do this or if anyone knows of another possible reason then i would be most grateful for your advice. it has been on a code reader and this has come back clear. many thanks, alan