Rent an auger if necessary
Go to the closest local store that rents power tools and ask about power augers.
Decide on a one-person or two-person model.
Select the correct auger bit attachment for the job. They come in diameters of 4-, 6-, 8- and 12-inches. For a 4×4 post, you’ll need an 8-in.-dia. bit. For a 6×6 post, a 12-in.-dia. bit works best. Keep in mind it’s extremely challenging to run a one-person auger with a 12-in. bit.