How to convert from raw pointer to shared_ptr

I have the existing code like this, how to convert it to use shared_ptr without using new/delete ?

B *ptr1;
C *ptr2;

// two constructor of class A
A::A():ptr1(nullptr), ptr2(nullptr) {}

A::A(std::istream *a) {
  ptr1 = new B(a);
  ptr2 = new C(*ptr1, *(this));
}
A::~A() {
  delete ptr1;
  delete ptr2;
}