What am I doing wrong? Password generator in Python using Tkinter and random

I started making a simple password generator in Python 3.8.1 using Tkinter and random, but I have a problem. I want to add checkboxes (in Tkinter: checkbuttons) but something is wrong. In the checkboxes, it would be possible to select the elements from which the password is generated. It is done in such a way that when you select a checkbox, a given pool of characters, e.g. letters or numbers, are added to the list of characters from which the password is generated. The problem is that when you uncheck the checkbox, the items are not removed from the character list and the password is still generated using the previous parameters.

import random
from tkinter import *
from tkinter import messagebox
import clipboard

# Define window
app = Tk()
app.geometry("305x155")
app.title("Password Generator")
# Items used to generate password
uppercase_letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
lowercase_letters = "abcdefghijklmnopqrstuvwxyz"
digits = "0123456789"
# From which items you want to generate password
upper = BooleanVar()
lower = BooleanVar()
nums = BooleanVar()

everything = ""

def check_1():
    global upper, lower, nums
    global everything
    # Add items what you want to everything variable
    if upper.get() == True:
        everything += uppercase_letters
    if upper.get() == False:
        everything.replace("ABCDEFGHIJKLMNOPQRSTUVWXYZ", "")
def check_2():
    global upper, lower, nums
    global everything
    if lower.get() == True:
        everything += lowercase_letters
    if lower.get() == False:
        everything.replace("abcdefghijklmnopqrstuvwxyz", "")
def check_3():
    global upper, lower, nums
    global everything
    if nums.get() == True:
        everything += digits
    if nums.get() == False:
        everything.replace("0123456789", "")

CheckboxLabel_1 = Label(app, text="Big Letters")
CheckboxLabel_1.grid(row=2, column=5)

CheckboxLabel_2 = Label(app, text="Low Letters")
CheckboxLabel_2.grid(row=3, column=5)

CheckboxLabel_3 = Label(app, text="Numbers")
CheckboxLabel_3.grid(row=4, column=5)

Checkbox_1 = Checkbutton(app, text="", variable=upper, onvalue = True, offvalue= False, command=check_1)
Checkbox_1.grid(row=2, column=6)

Checkbox_2 = Checkbutton(app, text="", variable=lower, onvalue = True, offvalue= False, command=check_2)
Checkbox_2.grid(row=3, column=6)

Checkbox_3 = Checkbutton(app, text="", variable=nums, onvalue = True, offvalue= False, command=check_3)
Checkbox_3.grid(row=4, column=6)

LengthText = Label(app, text="Length: ")
LengthText.grid(row=0, column=5)

Space = Label(app, text="")
Space.grid(row=0, column=4)

length = Entry(app, width=4) # Length of your password
length.insert(0, "20") # Default length (max. 62)
length.grid(row=0, column=6)

AmountText = Label(app, text="Amount: ")
AmountText.grid(row=1, column=5)

amount = Entry(app, width=4) # Amount of generated passwords
amount.insert(0, "1") # Default amount
amount.grid(row=1, column=6)

Generated = Label(app, text="Generated password:") 
Generated.grid(row=0, column=1)

Space_1 = Label(app, text="")
Space_1.grid(row=1, column=0)

PasswordText = Entry(app, width=25) # Text box
PasswordText.grid(row=1, column=1)

# Generating password function
def generate_password():
    PasswordText.delete(0, END) # Clear text box before writing a new password
    for x in range(int(amount.get())):
        password = "".join(random.sample(everything, int(length.get())))
        PasswordText.insert(0, password) # Past password into text box
    Completed = Label(app, text="Password generated.", fg="green") # Show info
    Completed.grid(row=3, column=1)

Submit = Button(app, text="Generate", command=generate_password) # Generating button
Submit.grid(row=2, column=1)

# Copying password to clipboard
def copytoclipboard():
    clipboard.copy(PasswordText.get())
    messagebox.showinfo(title="Info", message="Password copied to clipboard.")
    
Copy = Button(app, text="Copy", command=copytoclipboard) # Copying button
Copy.grid(row=1, column=3)

app.mainloop()

I used replace() to delete elements from everything variable because it's impossible to subtract strings.

Numbers and Big Letters checkboxes are unchecked, but the program still uses them to generate passwords (photo)