In C++, you can change the elements of a deque using the subscript operator [] or the at() method to access the element and then assigning a new value to it.

Here's an example of how to change elements in a deque using the subscript operator and the at() method:

#include <iostream>
#include <deque>

int main() {
  std::deque<int> d {1, 2, 3, 4, 5};
  
  // Change elements using the subscript operator
  d[0] = 10;
  d[3] = 40;
  
  // Change elements using the at() method
  d.at(2) = 30;
  d.at(4) = 50;
  
  // Print the elements of the deque
  for (auto it = d.begin(); it != d.end(); ++it) {
    std::cout << *it << " ";
  }
  std::cout << std::endl;
  
  return 0;
}

In this example, we create a deque d with five elements, and then we use the subscript operator and the at() method to change elements at different positions in the deque. We then print the values of all the elements in the deque.

The output of this program is:

10 2 30 40 50

As you can see, we have successfully changed the elements of the deque using the subscript operator and the at() method. Note that the same caution regarding the use of the subscript operator applies here as it does with accessing elements - the subscript operator does not perform bounds checking and can lead to undefined behavior if the index is out of range.