How to make a window that opens in place of another window, but so that it is not visible that the previous window has closed and the new one has appeared?

Question

C++ / C#

This Gif shows how it opens, it shows that the start window closes, and a new one opens in the same place.
And I need a new window to instantly open in the old one, like when switching slides instantly in a presentation.

Answer 1

The gif is crooked and stupid. To do this, you can use different methods.
1. Simple - tabs. Use PageControl to hide tabs.
2. More adequate, display frames on tabs
3. Simply use frames by switching the ones you need
And this is only part of the options

Answer 2

You can do all this in one window. For example, when you click on a button, hide all widgets (or whatever it is called in Sharpei), and dynamically create new ones and display them in this window. Or you can do something else: create panel1, place the background and buttons on it. Create another panel2 and place the "second window" gui elements. On the button, hide panel1 and show panel2.
There are +100500 methods to do this.