Pointers and references in functions - c++

Question

I have a problem with a school homework. I have to write a few function, and I have problem with the ShiftPointerVal which argument is a pointer to int. This is the most important in that homework, I mean that argument. I have that issue: error: lvalue required as left operand of assignment. Target of this function is to make a pointer bigger by one. I don't know how to write this function so the pointer to int can be an argument.
void ShiftPointerVal (int& pointer)
{
&pointer = &pointer + 1;
}
void ShiftPointerRef (int *&pointer)
{
pointer = pointer + 1;
}
void ShiftPointerPointer (int **pointer)
{
*pointer = *pointer +1;
}
int main ()
{
int number = 5;
int* p_number = &number;
std::cout << "\n----- 4 -----\n";
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
ShiftPointerVal (p_number);
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
std::cout << "\n----- 5 -----\n";
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
ShiftPointerRef (*&p_number);
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
std::cout << "\n----- 6 -----\n";
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
ShiftPointerPointer (&p_number);
std::cout << &number << "\t" << p_number << "\n";
std::cout << *p_number << "\n";
}