The relation between current and drift velocity of electron is $I = n e A v_d$ $n = \text{number density of electrons}$ $A = \text{cross-sectional area}$ $e = \text{charge of electron}$ $I = \text{current}$ $v_d = \frac{e E}{m l} \tau$ $E = \text{potential difference across the conductor}$ $\tau = \text{Relaxation time}$ $l = \text{length of the conductor}$ $\therefore I = n e A \times \frac{e V}{m l} \tau$ $R = \frac{V}{I} = \frac{m l}{n A e^2 \tau}$ As the temperature increases, the number of collisions increases and $\tau$ decreases and hence the resistance increases.