I hope your taking about just rounded sheetrock corners and not bull nosed tile corners.
If it's just round sheetrock corners, most are made of plastic and can be cut with an ossilating saw, hack saw or even a Dremel tool with a cut off blade and can be remove from where the wainscoting is going to be down to the floor. You make a through cut at the top of it then tap the wall on both sides of it down to the floor to beak up the drywall mud. Once it's off just install a steel right angle corner and finish it off.
A few rules when wanscoting.
Do not use that cheap prefinished paneling or anything that's made of compressed material. It will never stay laying flat and if it gets wet once it's trash.
Use only real wood beaded paneling or those vinyl stips.
If you use real wood, sand it before priming and painting, it will always have tiny wood burrs that will show if not sanded. Prime and paint it laying down if at all possible, the paint will level out better and there will be no runs in the low spots.
Never install it tight to the floor, floors are never level or flat. Lift it about 1/2" up off the floor.
Before deciding on what height to set it look around the room and check for wall outlets, window aprins, sink heights. You do not want the tops of the panels to make it so where an outlet cover is 1/2 of it comes out on top and 1/2 is below it.
It's best to start the panels in the middle of the wall and work your way out so the end cuts are equal. You must know where the studs are because where the seams sit have to be in the middle of a stud.
The first piece must be plumb, or all the other pieces will be out of level.
To attach the panels to a sheetrock wall we use Loc Tite Qwick Grip applyed in a tight S shape and press the panels tight to the wall with a hand floor roller. The only nails needed will be just two where the end seams area and at the top and bottom where the baseboard and chair rail or panel cap moulding will cover them up. If it's done right there should never be nails showing in the field.
For the two end pieces there going to have to measured and cut to size to make sure there 100% tight. If this part is done right there's no need for ugly inside corner moulding. Just a bead of Alex 50 year caulking is used. DO not use cheap painters caulking!