To measure out the size of the hole you will make, place the sump pump basin liner on the floor and trace around it using a permanent marker. Rent a jackhammer to break up the concrete floor inside the circle. Make holes with the jackhammer every couple of inches around the marked circle and use a large sledgehammer or a small sledge with a masonry chisel to further break up the concrete into small enough pieces that they can be easily picked up and disposed of. Keep some kind of large container, such as a heavy-duty trashcan, to cart away the broken-up concrete.
Wear heavy boots and safety glasses when operating a jackhammer.
Be sure you know how to safely and effectively operate a jackhammer. Follow all instructions for its use carefully.
If a jackhammer is unavailable, you can also try using a sledgehammer (as carefully as possible) to start the hole by breaking up the floor, and then a small sledge with a masonry chisel, or use a high-powered hammer drill with a large-sized masonry bit to make more precise cuts and to finish the work.
Using a pointed shovel, dig out the soil beneath the concrete to a depth of 2' or 3' and dispose of it. You want the top of the basin liner to fit flush at floor level when the job is complete, so be sure to match your digging depth as close as possible to the basin liner's dimensions. Add a small amount of gravel at the bottom of the hole, place the liner in the hole, and then use gravel to fill gaps around the liner to ensure a proper fit in the hole. This will also ensure good drainage. In the end, you want the top of the liner flush with the basement floor (top of the hole) with about 6" of space between the top of the hole and the gravel you added around the liner.
Mix and prepare a small batch of concrete according to manufacturer's instructions, and pour it onto the gravel layer in the basin until the space between the gravel and the basement floor has been filled. Smooth the concrete down with a trowel to make sure that the top of the basin and the surrounding floor is even and level. Let the concrete dry completely (check package directions for required dry times).