What a pulldown is:
It takes 24P and conforms it to 60i (29.97 with fields) – for a display context that refreshes field 1, field 2, field 1, field 2,… (which looks stupid on a display that does not,example a computer screen). Where a field here is every other scanlines.
A pulldown makes 5 frames from 4 by replicating two fields – just like the old analogue telecine. It does so by on 2 of the 5 frames take the odd (line 1,3,5…) of a frame and the even scanlines of another frame. The Upper or Lower here refers to where the previous and next frame scanlines get copied to that invented frame. In NTSC land where pulldown exists (25 FPS people like Europe don’t do that) you should for safety set the Pulldown to Lower first, since presumably in NTSC world the Lower scanlines are displayed 1/2 frame before the upper ones.
Pierre