Undoing Lightroom actions

I just downloaded the free trial, I'll probably be buying in a few days. Until now I've used Elements and its RAW module for PP.

Two questions about undoing actions in LR.

First, in the Develop module I have the history of actions done on the picture. Is there a way to select any step in the history list and delete it? I've tried right clicking on the step with no success.

Second, say I have edited a photo in Develop, selected other photos and edited them, etc. Later I go back to the first photo and want to undo some of the actions. In my limited playing around with LR when I do that and hit CTRL-Z, instead of removing the last edit step of that photo it switches to the last photo I had edited and removes the last action on that photo. I assumed the whole idea of nondestructive editing was the ability to retrace your steps if needed. I'm assuming I've done something wrong, so how do I undo edit actions on a photo that was previously edited?

Does THIS answer your questions?

Not really. I had learned about backtracking through the history by clicking on any given step. My first question was asked with the following example in mind. Say I have a picture that I crop, sharpen, adjust exposure, adjust saturation, and adjust white balance. Now suppose that I want to eliminate the sharpening step but keep everything else. If I click on the crop step in the history I deactivate the sharpening step but I have also deactivated all steps that were done after sharpening. I want to know if there is a way to delete the sharpening step but keep all subsequent steps active.

For my second question, your link tells me I can always just do a Ctrl-Z to eliminate a step which I'm familiar with and have used hundreds of times with Elements. But as I have played around with images in LR I haven't been able to do that. When I go back to a previously edited file in the Develop module and hit ctrl-Z the software doesn't delete that last edit done in the history of that photo, it switches me to the last photo I have edited and eliminates the last step of the history of that photo. I'm sure I'm doing something wrong here, maybe not having the older photo actually selected before I do ctrl-Z, but I haven't been able to figure out what I'm doing wrong.

You cannot delete a History step while leaving the later steps intact.