Answer: 16 times.

Dimensionally, Force is represented as $ [MLT^{-2}]$ and Length as $[L]$.

$\Rightarrow$ Energy $ = F\;d$ is represented as $ [MLT^{-2}] \times [L] = [ML^2T^{-2}]$.

Therefore, if Force and length are quadrupled in value, Energy $ = 4[MLT^{-2}] \times 4[L] = 16[ML^2T^{-2}]$.

$\Rightarrow$ the unit of energy increased 16 times.