I use an old curtain to handle these cacti. A sack would do the job as well. Wrap it (encircle the stem only so you can hold the ends of the curtain without being spiked) around at the halfway mark on the height and use it as a handle to hold the cactus. Try to wrap the older part otherwise you may break off some of the longer spines on the newer growth. Ease it down to the ground to lay horizontal. Now loosen the pot mix and free the roots of soil.

Use a larger pot for stability. Bring the plant back upright with the root ball in the pot. Another person would be useful. Pot it up and firm the mix, taking care to keep the plant fully upright and balanced. You may have to lean it against a wall for a few months until the roots become established enough to support the plant.