How do I migrate legacy code to C++14?

#include 
#include 
#include 

class LegacyClass {
public:
    void display() {
        std::cout << "Legacy class method\n";
    }
};

int main() {
    std::vector<:unique_ptr>> legacyObjects;
    for (int i = 0; i < 5; ++i) {
        legacyObjects.push_back(std::make_unique());
    }

    for (const auto& obj : legacyObjects) {
        obj->display();
    }

    return 0;
}