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In pygame, shapes can be updated by re-drawing them on the screen using the pygame.draw module functions. The process typically involves the following steps:

1. Create a pygame.Surface object to represent the screen or window to draw on.
2. Draw the initial shapes on the screen using the pygame.draw module functions (e.g. pygame.draw.circle, pygame.draw.rect, etc.).
3. Update the position, color or any other attributes of the shapes as required in the game loop.
4. Erase the previous shape by drawing a new shape with the same background color at its original position.
5. Draw the new shape in its updated position using the same pygame.draw module function as before.
6. Repeat steps 3-5 for each shape that needs to be updated in the game.

For example, to update a circle, you could do something like the following:

# Initialize pygame
pygame.init()

# Create a screen surface
screen = pygame.display.set_mode((800, 600))

# Draw an initial circle
circle_pos = (400, 300)
circle_radius = 50
circle_color = (255, 0, 0) # red
pygame.draw.circle(screen, circle_color, circle_pos, circle_radius)

# Game loop
while True:
    # Handle events and update game state
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()

    # Update the circle position
    circle_pos = (circle_pos[0] + 5, circle_pos[1])

    # Erase the previous circle
    pygame.draw.circle(screen, (0, 0, 0), circle_pos, circle_radius)

    # Draw the new circle
    pygame.draw.circle(screen, circle_color, circle_pos, circle_radius)

    # Update the display
    pygame.display.update()

This code updates the position of a red circle by moving it horizontally to the right by 5 pixels per frame. The previous circle is erased by drawing a new one in black at its previous position, and the new circle is drawn in red at its updated position. Finally, the display is updated to show the new circle.