You can do it once the plant goes dormant - late autumn - for best results. Dig up the root and split it with a spade or bread knife, depending on size, making sure each portion has some of the thickened roots and one or two of the growing point buds.
Replant each section in a well prepared hole with added garden compost and/or well rotted manure. Water in well and then mulch with a generous dollop of more garden compost or manure. Come spring, feed it some pelleted chicken manure or blood, fish and bone.
For the first year after division you need to be careful to take just a very few stems from each clump so that the leaves can feed the roots to build up a good strong plant for successive harvests. Never force a plant that is newly transplanted. However, once you have 2 or 3 good plants you can force them in rotation and enjoy the lovely tender, juicy pink stems every year.
More info from the RHS here - https://www.rhs.org.uk/advice/profile?pid=544
Agree with all of that, and did exactly the same when I set up a new bed last winter. Worth digging the area thoroughly to remove all the perennial weed roots, as the rhubarb will be there for several years. I had a fleece to hand (my friend keeps sheep and this one was too grotty to do anything else with) so I buried that as I dug, along with as much compost (it doesn't have to be very good) as possible. They love muck, and water too, and nettle feed if you can be bothered.
If you have a spare root or two heel them in somewhere as spares in case one doesn't take. If they all do you can give them away. I'd plant six if you have room, but at least three so you can force one every year.
This new bed is next to the compost heap so it gets all the run off from there, and quite sunny. Having done all of that they grew like Topsy this year and we even pulled a few stalks. This winter I shall force one of the crowns mercilessly and pick them all till the end of June.
Can't you taste the crumble already?
I lift mine every 3 to 4 years, split them in late autumn
They are left out over winter to catch the frost (I read that somewhere and it seems to work great)
Bury each split crown in early spring with plenty of manure
Only lift less that a third of the stems in the first two years
remove rotted leaves and stems to tidy things up
Always have several crowns to give away to friends