Connect the positive lead of your voltmeter on the positive lead of the charged electrolytic capacitor. Connect the negative lead of your voltmeter on the negative lead of the electrolytic capacitor. Turn on your voltmeter to measure the voltage across the capacitor.
Determine the value of resistor to discharge the capacitor with. Use larger values for a higher degree of safety. Use smaller values if you want to discharge the capacitor quickly. Follow guidelines for discharging a capacitor that the manufacturer might provide, usually about 5 to 50 Ohms per volt on the capacitor.
Multiply the capacitor value by the resistor value you plan to discharge the capacitor with. Then multiply this number, often referred to as the time constant, by 6 to determine the total time it will take to discharge the capacitor.
Place the resistor between the positive terminal of the electrolytic capacitor and the ground in your circuit. Use insulated pliers for this task and be careful not to inadvertently touch one of the resistor leads to the metal can of the capacitor or any other surfaces that are not at a ground point.
Watch the voltage on the voltmeter drop over time as the current stored in the capacitor flows out of the capacitor, through the resistor and back to ground (the earth). Wait until the voltage across the capacitor to ground reaches zero volts (which will take about 5 or 6 time constants). Conclude that the capacitor is discharged when the capacitor voltage reaches 0 Volt.
Make a voltage measurement between the capacitor's positive lead and the metal casing of the capacitor to ensure that there is not a voltage potential between the can and ground.