You might perform the following to remove a single element:
std::vector<int> vec;
vec.push_back(6);
vec.push_back(-17);
vec.push_back(12);
// Deletes the second element (vec[1])
vec.erase(std::next(vec.begin()));
Alternatively, to remove many elements at once:
// Deletes the second through third elements (vec[1], vec[2])
vec.erase(std::next(vec.begin(), 1), std::next(vec.begin(), 3));