That would be a "solid" lifter motor, and the adjustment is with shims on top of the lifter/in contact with the cam. There is a tool to depress the lifter buckets and another plier type tool to get the shim out. They should be marked on the bottom with their thickness(if installed correctly), so a thicker or thinner shim is replaced. Replacements can be purchased separately or kits can be(or used to be available).
The specs should be on a label on the underside of the hood, and once the motor is broken in, adjustment can be a annual/semi-annual thing.