unless you have adjustable control arms the only adjustment you have available is toe, which you adjust with the tie rods.
But you'll also need to make sure there are no worn bushings, wheel bearings, ball joints, struts, etc. That will affect a lot of things and you can't "adjust" mechanically worn parts enough to be safe/comfortable to operate.
to adjust toe, you need to roll the ATV forward about 10 foot or so on flat ground (shop floor works) and stop, lock the brakes or keep it from rolling backwards. Make sure the wheels are pointing straight ahead. I just drive it across the floor and line it up with one of the expansion joints. Adjust toe so that front is about 1/4" shorter than the rear. You can go to zero if you want but it makes little difference as it changes with suspension movement anyway.
a lot of people will eyeball them and it is rarely close. Some guys can get real close, but I don't trust my eyes. I can make it "look" perfect. Get the tape measure out and it's 2" off. While on that, measuring can be a bear because the lugs on some tires are asymetric. "Most" are symetrical enough to make it work, and most have a center mold line. Hook the tape measure on the same lug front and rear, and use the mold line to take the measurement.
pavement kills tires, period. Hard pack does as well (dirt roads). Try to avoid those if possible.
also make sure your 4x4 is fully disengaging on both sides. And brakes. I've seen a few older sportsmans lately that the old brake fluid has congealed and is causing the caliper(s) to stick. Fluid won't back up in the master cylinder so as you ride, and the front rotor(s), the pads, etc all heat up and expand, they'll apply pressure-causing drag. Sometimes it's unnoticed. I'd highly suggest flushing the brake fluid if it hasn't been done. If they're sticking like that, hopefully the flushing will solve it. If not, may have to put a master cylinder on it, if it's still available. Some of the older ones are NLA.
The newer ones use a slightly different design/different suspension geometry, and possibly a totally different design for the AWD system depending on which one you have.
road crown on paved and hard pack surfaces doesn't help any, which is usually why one side wears more than the other.