Buy a cactus from the nursery, or order it online.
Put on your gloves after you have assembled your tools.
Dig a shallow hole for the cactus. They do not have deep roots. You should dig a little lower than the roots of the plant, but you don't have to go down much more than a few inches.
Set the cactus pot on its side, and gently start tapping to loosen it from the pot. Most larger cacti will come out of the pots fairly easily. If it doesn't, you may have to use a utility knife to cut the plastic on the pot, and gradually remove the root ball from the pot that way.
Set the cactus in the soil by holding it from the root ball, and push back the original soil until the hole is filled up.
Lightly water it. Depending on our climate, you may need to water it once a week, or once a month. Cacti do not need much water at all.
Buy a cactus, a slightly larger pot than the one that it is already in, and cactus potting soil.
Put the cactus soil in the pot, leaving about 1/2-inch space at the top. Lightly tap the soil down.
Tap on the original pot to gently remove it from the pot.
Make a hole in the soil with your fingers that is big enough to accommodate the new cactus and its existing soil.
Place the cactus in the hole in the pot, and water lightly.
Set in a sunny spot outside, but bring it in when temperatures threaten to go below 40.