The speed of the pendulum is dependent on the length of the pendulum and the angle of displacement.
On increasing the length of the pendulum and the angle of displacement, the extreme position of the pendulum increases, or displacement from its mean position increases.
This results in an increase of potential energy at the extreme points.
When the pendulum bob reaches the mean position, all the potential energy gets converted to kinetic energy.
This increase in kinetic energy results in increased speed.
Thus, the speed of the pendulum can be increased by increasing the length and the angle of displacement from the mean position.