Turn power off, use 2200 ohm resistor to short the capacitor terminal to ground. Mark the wires per terminal, remove wires and capacitor. Replace with an identical capacitor, reinstall wires.
If you are sure that the capacitor needs to be replaced. First you will need to purchase the replacement part for your unit, remove all fuses and power to the unit. Remove the protective covers and from there replacement should be simple. Make sure you discharge the charge in the old capacitor or you will receive a shock.
Get an exact replacement, matching capacitance and voltage. Disconnect the power (breaker) and remove the wires. Wire in a new capacitor the exact way the old one was removed.
First make sure power is off to the unit,next draw yourself a diagram of the wires going to the capacitor and buy your replacement part from a dealer in the same brand as your unit as some newer or upgraded parts may not look the sanme as yours
If the capacitor on the condenser is not working, remove one of the leads and place a multimeter between the lead and the cap. Turn on the system to see if you have any capacitance. If the cap will not hold a charge, disconnect the other leg of the capacitor and replace it.