How to Change the Tkinter Label Font Size

import tkinter as tk
import tkinter.font as tkFont

app = tk.Tk()

fontStyle = tkFont.Font(family="Lucida Grande", size=20)

labelExample = tk.Label(app, text="20", font=fontStyle)


def increase_label_font():
    fontsize = fontStyle["size"]
    labelExample["text"] = fontsize + 2
    fontStyle.configure(size=fontsize + 2)


def decrease_label_font():
    fontsize = fontStyle["size"]
    labelExample["text"] = fontsize - 2
    fontStyle.configure(size=fontsize - 2)


buttonExample1 = tk.Button(app, text="Increase", width=30, command=increase_label_font)
buttonExample2 = tk.Button(app, text="Decrease", width=30, command=decrease_label_font)

buttonExample1.pack(side=tk.LEFT)
buttonExample2.pack(side=tk.LEFT)
labelExample.pack(side=tk.RIGHT)
app.mainloop()

fontStyle = tkFont.Font(family="Lucida Grande", size=20)

def increase_label_font():
    fontsize = fontStyle["size"]
    labelExample["text"] = fontsize + 2
    fontStyle.configure(size=fontsize + 2)

labelExample["text"] = fontsize + 2

import tkinter as tk
import tkinter.font as tkFont

app = tk.Tk()

fontfamilylist = list(tkFont.families())

fontindex = 0

fontStyle = tkFont.Font(family=fontfamilylist[fontindex])

labelExample = tk.Label(app, text=fontfamilylist[fontindex], font=fontStyle)


def increase_label_font():
    global fontindex
    fontindex = fontindex + 1
    labelExample.configure(
        font=fontfamilylist[fontindex], text=fontfamilylist[fontindex]
    )


buttonExample1 = tk.Button(
    app, text="Change Font", width=30, command=increase_label_font
)


buttonExample1.pack(side=tk.LEFT)
labelExample.pack(side=tk.RIGHT)


app.mainloop()

fontfamilylist = list(tkFont.families())

labelExample.configure(font=fontfamilylist[fontindex], text=fontfamilylist[fontindex])