do what nextdesign said, if the reduce function doesn't give desirable results go to edge selection mode and start selecting edge loops and deleting edges
(ctrl + right click to bring up edge selection, or double click if you're in 2009 to select an edge loop, shift+right click to bring up delete edge, this will delete the edges and the associated vertex if possible)

you may end up having to insert more edges to delete some to retain the shape of your model