When you want to change a variable you can use code like this –

x = 4
x = 9 
x = x + 1
print x

To change an array you need to access an individual element within the array first before you make a change.

numbers = [5,2,1,7,1]
print numbers
numbers[3] = 20
print numbers

Do you see that the 7 has changed into a 20? This is because 7 is at position 3 in the array (remember that it always starts from 0). Change the above code so that the 2 becomes a 90!