The center of lift is a point on the wing where the lift can be thought of as concentrated. The center of mass is where the weight of the system is focused. On a sport parachute the weight is clearly centered well below the wing, in the form of the pilot. By changing the relative position of the center of mass to the center of lift, the pitch of the canopy can be affected, changing the angle of attack. Many skydivers think angle of attack means the angle of the parachute relative to the ground.
Angle of attack is the angle of the chord line to the apparent wind.
Changing the angle of attack is done by applying leverage against the wing. An aircraft does this with its tail section but parachutes lack this capability. Flaring is the only way to make a change in a canopy's angle of attack. The result is that the angle of attack temporarily increases, generating more lift through greater deflection of air. Note that in a flare, the changed angle of attack is due to an actual change in the apparent wind felt by the canopy as the weight below it swings forward - a lever action against the wing just like a hang glider flare.