how to change character in string python

mytext = 'Hello Zorld'
mytext = mytext.replace('Z', 'W')
print mytext,

string.replace(old, new, count)

>>> s = list("Hello zorld")
>>> s
['H', 'e', 'l', 'l', 'o', ' ', 'z', 'o', 'r', 'l', 'd']
>>> s[6] = 'W'
>>> s
['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']
>>> "".join(s)
'Hello World'

# Python3 program to demonstrate the  
# use of replace() method   
  
string = "geeks for geeks geeks geeks geeks" 
   
# Prints the string by replacing geeks by Geeks  
print(string.replace("geeks", "Geeks"))  
  
# Prints the string by replacing only 3 occurrence of Geeks   
print(string.replace("geeks", "GeeksforGeeks", 3))