high/low or range shift lever

My Craftsman Lawn Tractor model 917.273090 has a high/low lever called a range shift lever on the manual diagram, on the right side. I can shift into the 3 forward gears and reverse with no problem, but the high/low lever is stuck in the up position. I assume I would shift with the clutch in, but that doesn't help.
Is there a way to unstick this lever so I can have more range in my gears?
Thanks