Why not change classes in the kv file when you press the button?

Good time of day.Why not change classes in the kv file when you press the button?I push the button and in fact,should be a transition between classes.That is,the main function now returns instead of a class wirtul,the widget class and Vice versa.But this is not happening,or rather not display the window itself.Tell me what it is and how I can implement my idea?Thanks in advance!
Here is the code of the file .py:
from kivy.app import App
from kivy.uix.widget import Widget
from kivy.lang import Builder
class Wirtul(Widget):
pass
class Widgets(Widget):
pass
presentation = Builder.load_file("SimpleKivy.kv")
class SimpleKiv(App):
 def build(self):
 return presentation
if __name__=="__main__":
Myapp=SimpleKiv()
 Myapp.run()

and this file SimpleKivy.kv
<widgets>:
name:'main'
Button:
size:self.minu_ki
pos:0,0
 text: "chit"
 color: 0,1,0,1
 font_size: 40
 on_release:app.root.current = 'high'
<wirtul>:
name:'high'
Button:
 size: 170,75
 pos: 100,0
 text: "naz"
 color: 1,0,0,1
 font_size: 40
 on_release: app.root.current = 'main'</wirtul></widgets>
June 10th 19 at 14:40
0 answer

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