Replacing a sump pump

Most sump pumps are installed with a rubber coupling to connect the piping to the exterior to the piping screwed into the pump.
Remove the sump pump cover, loosen the rubber coupling. Lift the pump out of the sump crock. Transfer the piping to the new pump, sit new pump in the crock, reconnect to the piping with the rubber coupling and plug pump in.

It can be a simple as that but seldom is because things don't always line up or fit exactly. Usually a little bit of reconfiguring of the piping is required. That is not usually a problem because most piping is PVC.

There should be a check valve on the discharge line, you should try to disconnect the drain below the check valve to prevent a lot of unwanted sewer dumping back out of the vertical drainline. It can get messy so be prepaired for some extra cleanup.

Read your installation instructions on the new pump, many have built in check valves.