Chevrolet 2010 Impala Owner's Manual page 154

If cruise control is set at a desired speed and then the
brakes are applied, the cruise control is disengaged
without erasing the set speed from memory.
Once the vehicle speed is 40 km/h (25 mph) or
greater, press the +RES button on the steering wheel.
The vehicle returns to the previously selected speed
and stays there.
If the cruise control system is already activated,
Press and hold the +RES button on the steering
wheel until the desired speed is reached, then
release it.
To increase vehicle speed in small increments,
press the +RES button. Each time this is done,
the vehicle goes about 1.6 km/h (1 mph) faster.
4-8
If the cruise control system is already activated,
Press and hold the SET button on the steering
wheel until the lower speed desired is reached,
then release it.
To slow down in small amounts, press the SET
button briefly. Each time this is done, the vehicle
goes about 1.6 km/h (1 mph) slower.
Use the accelerator pedal to increase vehicle speed.
When you take your foot off the pedal, the vehicle will
slow down to the cruise speed you set earlier.