I'll show you how to sort vectors in ascending or descending order. Include the algorithm library and call sort(v.begin(), v.end()) to sort the entire vector in ascending order. This uses quicksort internally and runs in O(n log n) time.
To sort in descending order, use sort(v.begin(), v.end(), greater()) which takes a comparison function. You can sort part of the vector with sort(v.begin() + 2, v.begin() + 5) to sort only indices 2 through 4.
To reverse a sorted vector, call reverse(v.begin(), v.end()). Sort modifies the original vector, so make a copy first if you need the original order.