How does constant gravitational acc. Act upon body moving upwards.

when a body moves upwards gravity tries to attract the body towards the centre of the earth threfore the speed of the body while it moves up decreases and becomes zero at certain height than starts to increase when it comes down. the acceleration due to gravity is constant 9.8 m/sec2 when it moves down towards the earth and it becmoes -9.8m/sec2 because it going opposite to the earth....