1. Die Hard (1988)
2. Die Hard 2 (1990)
3. Die Hard with a Vengeance (1995)
4. Live Free or Die Hard (2007)
5. A Good Day to Die Hard (2013)
However, many people prefer to watch the movies in the order of their release, which is as follows:
1. Die Hard (1988)
2. Die Hard 2 (1990)
3. Die Hard with a Vengeance (1995)
4. Live Free or Die Hard (2007)
5. A Good Day to Die Hard (2013)
Ultimately, the order in which you watch the Die Hard movies is up to you.