Moving an Object Around not Working Pygame Code Check

Question

I have been following a tutorial on how to move and image around, when I run my code, I get this error:

Traceback (most recent call last): File "C:\Users\krzys\Desktop\Dawid Grubba\Private\Game creating\Hero Jump\Hero Jump.py", line 142, in Menu() File "C:\Users\krzys\Desktop\Dawid Grubba\Private\Game creating\Hero Jump\Hero Jump.py", line 135, in Menu button("Play", 120, 350, 200, 100, green, bright_green, "Start") File "C:\Users\krzys\Desktop\Dawid Grubba\Private\Game creating\Hero Jump\Hero Jump.py", line 65, in button In_Game() File "C:\Users\krzys\Desktop\Dawid Grubba\Private\Game creating\Hero Jump\Hero Jump.py", line 110, in In_Game y += y_change UnboundLocalError: local variable 'y_change' referenced before assignment

I have replaced the y with x but it still displayed the same massage but with x. This is the website: https://pythonprogramming.net/pygame-tutorial-moving-images-key-input/

This is the main part of my code which I want you to view to answer this question:

def In_Game_Earth_Image(x,y):
    gameDisplay.blit(Earth_Image, (x,y))

def Title():
    message("Hero Jump")

Character1=pygame.image.load("Normal Character.png")
Character1=pygame.transform.scale(Character1, (100,150))

def Starting_Charcter(x,y):
    gameDisplay.blit(Character1, (x,y))

y_change = 0

def things(thingx, thingy, thing_width, thing_height):
    gameDisplay.blit(RockImg,[thingx, thingy, 20, 20])

def button(msg, x, y, w, h, ic, ac, action=None):
    mouse = pygame.mouse.get_pos()
    click=pygame.mouse.get_pressed()

    if x+w > mouse[0] > x and y +h > mouse[1] > y:
        pygame.draw.rect(gameDisplay, ac,(x, y, w, h) )
        if click[0]==1 and action != None:
            if action=="Start":
                In_Game()
            elif action=="quit":
                pygame.quit()
                quit()
    else:
        pygame.draw.rect(gameDisplay, ic,(x, y, w, h) )

    smallText=pygame.font.Font("freesansbold.ttf", 20)
    textSurf, textRect=text_objects(msg, smallText)
    textRect.center=( (x+(w/2)), (y+(h/2)))
    gameDisplay.blit(textSurf, textRect)

    pygame.display.update()

Earth_Image=pygame.image.load("Ground_Image.png")
Earth_Image=pygame.transform.scale(Earth_Image, (900, 600))

def In_Game():
    x=50
    y=250

    In_Game_Earth_Image(0,0)

    thing_starty =265
    thing_startx= 1200
    thing_speed=-7
    thing_width=10
    thing_height=10

    Crashed=False

    while not Crashed:

        for event in pygame.event.get():
            if event.type==pygame.QUIT:
                pygame.quit()
                quit()

            if event.type==pygame.KEYDOWN:
                if event.key == pygame.K_SPACE:
                    y_change=-20
            if event.type==pygame.KEYUP:
                if event.key==pygame.K_SPACE:
                    y_change=0

        y += y_change

        In_Game_Earth_Image(0,0)
        Starting_Charcter(x, y)
        things(thing_startx, thing_starty, thing_width, thing_height)
        thing_startx += thing_speed

        if thing_startx < -300:
            thing_startx = 1000
            thing_starty = 265

        pygame.display.update()
        clock.tick(60)

def Menu():
    Menu=True

    while Menu:
        for event in pygame.event.get():
            if event.type==pygame.QUIT:
                pygame.quit()
                quit()

        Title()

        button("Play", 120, 350, 200, 100, green, bright_green, "Start")
        button("Quit", 570, 350, 200, 100, bright_red, red, "quit")

        pygame.display.update()
        clock.tick(15)

gameDisplay.fill(white)
Menu()

pygame.quit()
quit()

I probably made a silly mistake but I ten I am a bit of a noob with pygame. Thank you for all your help.