Eventually you might have the need to upgrade your MySQL installation. When doing so, it's important to consider what type of upgrade you'll be making. If you are staying within the same release series, going from, say, 4.1.12 to 4.1.17 or from 5.0.3 to 5.0.4, that's a relatively safe upgrade. If you are changing the release series, 4.0.9 to 4.1.12 or 4.1.17 to 5.0.18, there's a bit more to it.
The first type of upgrade is best if you want the latest, most stable and secure version, without any hassle. The second type of upgrade is normally for the benefit of adding features but has a higher potential for problems. MySQL recommends jumping only a single release at a time (3.23 to 4.0, 4.0 to 4.1, 4.1 to 5.0, and so on).
The MySQL manual covers the specifics of upgrading from one version of MySQL to another in great detail so that you can be best prepared as to what you might encounter. The directions I give next are more generalized recommendations.
To upgrade MySQL: