I've done this before and I can't do it again - either I've triggered some setting that changes how scale (or extrude) works or I've just completely forgotten how to do this. I have the cylinder on the right and need to make it like the one on the left, but the final measurements are rather different, so I can't just scale the one on the left. I tried to extrude the vertices on the upper level (on the cylinder on the right), then right click (to break out of the extrude mode) and change to scale so I could scale them inwards. When I do that, I get results like this: That looks to me like it's still trying to extrude all the vertices and not like it's trying to scale them.
Have I activated some mode that doesn't let me scale normally? How can I just extrude those top vertices inwards (or outwards if I start from the narrower cylinder)? I tried using I and I got the shape I wanted, but the measurements were off from what they should have been.