A sump pump replacement is a job you can follow in order. Each step ends with a check you can see. The old pump's age is a planning input for the swap. Write down its manufacture date before you lift it out, so the next replacement lands on the calendar.
Start with the pit. Note its width and depth, the discharge pipe size and where it exits the house, the outlet the pump plugs into, whether the outlet is protected by a GFCI, the type of float, and whether there is a check valve in the discharge line. Confirm the power source. If the pump is wired directly into the house circuit rather than plugged into an outlet, that connection is a licensed electrician's task. Otherwise, unplug the pump from its outlet before you touch anything in the pit.
Lift the old pump out by its handle or its discharge fitting, and keep the cord clear of the pit edge. Note the discharge fitting size and whether the check valve has an arrow showing flow direction. Clean the pit of sediment, gravel, and debris, and look at the pit liner for cracks or loose sections.
Set the new pump on the pit base so it sits level and clear of the walls. Connect the discharge pipe through the check valve. Place the valve so its arrow points away from the pump, toward the discharge exit. Tighten the fittings by hand first, then a little more with a wrench, without forcing them.
Set the float so it can move freely. A float that rubs the pit wall or the discharge pipe will start and stop at the wrong times. Tie the cord loosely to the pit's support so it cannot pull the pump or the float out of position when the pit fills.
Plug the pump into its outlet and run the test. Pour water slowly into the pit until the float rises. Watch the pump start, pump the water down, and shut off on its own. Confirm that the discharge water flows away from the foundation and does not drain back into the pit. Test the GFCI outlet with its test button. If the house has a backup pump or battery system, test that too.
Close the job with a short record. Write down the pump model, the install date, the test result, and the manufacture date of the new pump. Keep that page with the house papers so the next planning date is easy to find.