\[(2 + m)^{2}(2 - m)^{2} =\]
\[= (2 + m)(2 - m)(2 + m)(2 - m) =\]
\[= \left( 4 - m^{2} \right)\left( 4 - m^{2} \right) =\]
\[= \left( 4 - m^{2} \right)^{2} = 16 - 8m^{2} + m^{4}.\]