If your Ford Focus has a manual transmission, it has a master cylinder that contains fluid for the clutch, which is similar to the brake master cylinder (they both even use the same hydraulic fluid). This cylinder is mounted directly behind the clutch pedal in the driver's compartment; you need access to this space and the engine compartment to remove the cylinder. The exact removal process can vary depending on the year of the car.
Disconnect the car's negative battery cable. On most models, the cable is held onto the terminal with a clamp; loosen the clamp nut with an insulated wrench.
Push the driver's seat back as far as it will go and then unscrew the fasteners for the lower dash trim panel in that area using a screwdriver. Remove the panel and unclip the diagnostic connector plug from the panel.
Lay clean rags below the clutch pedal in anticipation of hydraulic fluid spilling during the procedure.
Raise the car's front end with a floor jack and support it on axle stands to access the fluid connections at the engine compartment's firewall.
Pull out the securing clip at the top of the fluid supply connection; this is the larger pipe and is accessible from either the engine compartment or below the car. Pull the pipe fitting out of the master cylinder--watch out for spilling fluid--and plug the hose end with a rubber plug.
Release the smaller fluid pipe from its support bracket near the firewall, then disconnect it in the same manner that you disconnected the larger hose.
Disconnect the cylinder's pipe flange from the firewall; this requires removing its nut with a wrench or pulling out the U-shaped clip and can only be done from the driver's compartment. Remove the two bolts securing the cylinder to the pedal bracket.
Unclip the master cylinder from the from the pedal bracket in a sideways direction and pry off the piston rod at the top of the clutch pedal. Remove the cylinder from the footwell; make sure you don't tilt it so no more fluid will spill.
