Sorry in advance for the probably basic question:
I have created a solid via the following steps:
* create a rectangle (e.g. 30x20, centered around 0,0,0)
* create another rectangle (e.g. 20x10 100mm away though centered around 0,0,100)
* lofting these two rectangles to get a solid cuboid
* delete the two construction rectangles

Now a little later I decide that I want to change the size of the 30x20 side to 40x20. My attempts so far:
* selecting the solid and clicking on "Show pts." to move the points up - but show pts. isn't working
* selecting the 30 mm long upper edge, trying to drag this up - doesn't move
* selecting the 30x20 face, try using the 1d and 2d scaling tools selecting the base as center, trying to scale the face - nothing happens

The only way how I could manipulate the solid was to use scale on the entire solid. But that way I can only change the overall height, not the height on one side.

Is there something I could do? Or is the only way to do this to throw the solid away and remake it from scratch if I already deleted the lofted original rectangles (or did other operations in between that deleted the history)?

Edit: added the cuboid 3dm for reference. (dimensions are 210x55 and 130x35 and the distance 1000 in this example but the concept is the same. Let's say I want to change the 210x55 side to 200x55)

Edit2: I separated the solid, now I could select the points again. But the control points for the two rectangles weren't on the corners but again a much wider plane. Why can't those just be the corners of the rectangle itself - then show points would probably also have worked? I'm apparently still struggling to get the logics behind some construction steps.

Edit3: Here a second iteration where I manually deleted the faces with the big construction planes and added faces instead. These have the control points as expected directly on it's corners. If I join these faces again, I get a solid where I can edit the points as expected.
Wouldn't it be better if the result of the loft would be something along the lines of this second object? What is the advantage of these big planes?