how can I determine if an templated integer type signed or not? how to convert between them?

I have a template function which takes an integer type, such as:

template<class IntType>
IntType foo(IntType value)
{
    IntType ret;

    // As I may need to do 64bit operations,
    // so I would like the return type same as the input type 
    ......;
    return ret;
}

In the function I need to do bitwise shift operations on value. As right shift is different between signed and unsigned integers, so I need to convert between signed and unsigned types. It seems I cannot use either std::is_unsigned and std::make_unsigned, could anyone please tell me how can I make a template type to unsigned? Thank you!