Clutch fluid is nothing more than conventional brake fluid. It will absorb moisture from the air, so it should be flushed on a yearly or bi-annual basis. Otherwise, the moisture can contaminate and damage the clutch hydraulic system.
To replace the clutch fluid, it is first removed from the clutch fluid reservoir. Then the reservoir is cleaned and fresh fluid is added. The clutch pedal is then pressed and the clutch master cylinder generates pressure, forcing fresh fluid out to the clutch slave cylinder.
Brake fluid will damage a vehicle's paint, so avoid contact with the surface of the car.
Mechanics' Corner: More Technical Detail
If the brake fluid reservoir is shared with the clutch, follow the brake bleeding procedure. However, only the bleed screw at the clutch slave cylinder should be opened to flush out the brake fluid.
If the clutch has a dedicated fluid reservoir, attach the brake bleeder there and proceed as noted above.
Note: Access to the bleeder screw at the clutch slave cylinder can be difficult on some vehicles.