As stated, up for 4WD, down for 2WD, but there's also a diagram on a sticker next to the lever - at least my 3410 has such. I do not need to stop or shift into reverse to switch from 4WD to 2WD and visa versa, just to go slow and gently push/pull on the lever. Under your other foot (right foot) is the rear wheel lock lever, stomping on that (which is a bit awkward) while in 4WD is about all the traction your tractor will be able to muster (i.e., if stuck and that doesn't work, it's time to use the FEL).