You first want to make sure its not coming from a conduit that comes out of the foundation and into the switch. If it is, you need to remove that conduit and patch the foundation. If it is the switch itself, you need to replace it. Shut the power off at the circuit breaker and get yourself some electrical meters and check for voltage to be sure that it is off. You then need to turn on some faucets and drain the tank. When its drained, the gauge on the tank should read zero. Next step is to shut the main valve going to the house get a bucket,put it underneath the spigot on the tank , and open it to drain the water left in the pipe. Next you need to un wire the switch, get both the wires from the panel and the wires going to the pump out of the switch. With a wrench remove the switch and replace it. If the nipple stays in place then put some plumbers tape and pipe dope on the threads and simply screw the new switch on. If the nipple comes off with the switch, then you will have to remove the nipple from the old switch,do the tape and pipe dope on both ends of the nipple,and install the switch. Wire the switch by screwing the leads from the breaker on the outside lead terminal screws and the pump leads on the inside terminal screws. If you have a 30/50 or 40/60 switch you need to adjust the air in the tank so the pressure is 2lbs below the cut in pressure. Once that is all done, shut your drain spigot off at the tank and turn the power back on. the pressure should build to its shut off pressure. Turn the water on slowly to the house and the pressure will start to drop. If all your settings are right, it should cut in at the switches set cut in pressure. Once it cuts in shut the water off to gthe house and make sure it builds to the correct pressure. If it does just turn the valve back on, shut your faucets off and you are good.
If you are not sure about doing any of that, you should call a pump guy.
sammy
www.tylerwellandpump.com