There is a lever just under the seat and to the righthand side of it (basically between the seat and the right fender). With the motor revved up some, pull the lever up and the lift *should* come up. If not, check to see whether or not the rockshaft valve might be closed off. It's the round knob probably directly under the front of the seat. It's normally used to adjust the rate of descent of the attachments (each one weighs differently you know) but on most tractors it can also close off the valve controlling the lift.
If that doesn't get it up, then there might be a problem with the hydraulics.