Dashboard > Sliders > All sliders
And choose the slider that you want to edit. Then click on Add new slide
This will open a block editor that you can use to enter and edit the content of your slide. Almost all Gutenberg block are supported and the only limit is your imagination.
Slider height is a conseguence of each child slide height. So if you want your content vertically aligned with space on top and bottom, just add a
Spacer block like in this example: