You can control the vector head size by typing a new value into the Head size text field, which is the fraction of the entire vector's length that will be devoted to the vector's head. Vectors in the Vector plot can be drawn without vector heads so that only the line part of the vector glyph is drawn. This results in cleaner plots, but the vector direction is lost. To turn off vector heads, uncheck the Draw head check box at the bottom of the Vector plot attributes window.