In order to obtain high capacitance, plats of large area should be taken and kept close to each other.
The capacitance of a parallel plate capacitor of plate area A and the distance d, between the plated is given by

$c = \frac{K \epsilon_o A}{d}$ Given, $d_1 = d$, $d_2 = \frac{d}{2}$, $K_1 = K$, $K_2 = 2K$ $\frac{C_1}{C_2} = \frac{K_1}{d_1} \times \frac{d_2}{K_2}$ $= \frac{K}{d} \times \frac{\frac{d}{2}}{2 \times K}$ $\frac{C_1}{C_2} = \frac{1}{4}$ $\Rightarrow C_2 = 4 C_1$ Hence, capacitance increases four times.