Here is what you need:

Torch/Cigarette Lighter

Pad Prick

Pad Slick/Leveler Tool

Pad and Cork Cement

Cloth

Q-tip

Alcohol

Feeler Gauge

Remove the key(s) that need new pad (s). This may be a several step process.

Remove the leaking pad by heating the pad cup without scorching the key. When the cup is warm, remove the pad using the pad prick. Remove any shellac or hot glue in the cup by heating it with your torch and wiping it clean with a rag, or a Q-tip -alcohol may be helpful here and this is a good time to clean the rods and screws with alcohol.

NOTE: Never let a heated cup with the pad removed rest on the tone hole. It will instantly melt a plastic tone hole and can scorch a wooden one.

Fit a new pad to the pad cup.

Squeeze enough pad and cork cement into the pad cup to lighly cover the bottom and spread it evenly.  Also squeeze some on the backside (cork side) of the pad and spread it out evenly.  Pay close attention here - too much cement makes a mess and too little may result in pads falling out.  Place the pad into the cup and add a little oil in the right spots (friction areas).

Check the new pad for leaks with your feeler gauge. You can make a simple gauge with an old reed and cellophane paper from a cigarette pack or candy package.  Cut the reed down the middle, then cut 1/16" W x 1/2" L candy wrap and glue it to the the tip of the reed. This will be your gauge when it's dry - the reed is your handle.

Use your feeler gauge to check resistance. Using a clock for reference, check the 12.00/6.00 and 3.00/9.00 points. You should feel resistance at all points. If the 12.00 point is not touching you need to use your pad slick to apply pressure to the 6.00 point and the same for the 3.00/9.00 points. Some pads will seat with little or no adjustments, others can be a bit more challenging - be patient! Give the cement at least 12 hours to dry properly before you play/test the instrument. If you need to re-seat a pad, heat can also be added to the pad cement. You would need to hold a cigarette lighter close to the pad cup but with the tip of the flame held away from the body (requires care and caution)

Your goal is simply to get the pads to sit evenly on the tone holes - all leaks must be removed in order to have a playing instrument.