Not sure how you could split it. Instead, have you considered training it to climb a moss pole? Doing so would help it grow more upright and less bushy.

A moss pole would help it grow more upright. You would just tie the main stalks to the pole to train it.

It does look like you have at least two main stalks in the pot growing in opposite directions. If the stalks go into the soil individually (not branched) it is likely there are actually multiple plants in the pot. To seperate this you would just pull the entire thing out of the pot and use your hands to split the roots apart that go with each plant, you may need to end up cutting some roots, which is perfectly fine. As these Monstera grow, they almost always need some form of support to look nice if not cut back. Their natural growth pattern is to vine up trees so they grow more upright/long instead of short and bushy.

Ax, hatchet, machete, pruning saw, spade, will all work equally well, but it's really hard to beat a 15", 1 lb cutter mattock with this head configuration for dividing.

Al

You don't need to split it up, my Monstera has several vines all growing together just fine. What it needs is support. Monsteras are vining plants that can't grow upright on their own.