WARNING: - Always backup your database data before upgrading. From the command line you can do this with the mysqldump command.

eg:

mysqldump -u[username] -p[password] [database_name] > [filename]

This will dump the contents of the specified database into the specified filename.

If an error occurs you can re-create your previous database by just importing your backed up database data. You'll need to drop and recreate your database (or remove each table).

mysql -u[username] -p[password] [database_name] < [filename]

Upgrades may take several minutes depending on the size of your database.