How can I sort generic list DESC and ASC?

With Linq

var ascendingOrder = li.OrderBy(i => i);
var descendingOrder = li.OrderByDescending(i => i);

Without Linq

li.Sort((a, b) => a.CompareTo(b)); // ascending sort
li.Sort((a, b) => b.CompareTo(a)); // descending sort

Note that without Linq, the list itself is being sorted. With Linq, you're getting an ordered enumerable of the list but the list itself hasn't changed. If you want to mutate the list, you would change the Linq methods to something like

li = li.OrderBy(i => i).ToList();

without linq, use Sort() and then Reverse() it.

Without Linq:

Ascending:

li.Sort();

Descending:

li.Sort();
li.Reverse();