We can use three methods to upgrade our oracle database:

• Export/Import
• DBUA
• Manually by using Scripts

Export/Import
Export/Import utilities only physically copy data from current database to a new database. The current database's Export utility copies specified parts of the database into an export dump file. Then, the Import utility of the new Oracle Database loads the exported data into a new database.

Database Upgrade Assistant
The Database Upgrade Assistant (DBUA) utility configures the database for the new Oracle Database. The Database Upgrade Assistant automates the upgrade process by performing all of the tasks normally performed manually.

The Database Upgrade Assistant performs the following pre-upgrade steps:
· It checks for any invalid user accounts or roles
· It checks for any invalid data types
· It checks for any disported character sets
· It checks for adequate resources, including rollback segments, table spaces, and free disk space
· It optionally backs up all necessary files

The Database Upgrade Assistant does not begin the upgrade until it completes all of the pre-upgrade steps.

The Database Upgrade Assistant automatically modifies or creates new required tablespaces, invokes the appropriate upgrade scripts, archives the redo logs, and disables archiving during the upgrade phase.

While the upgrade is running, the Database Upgrade Assistant shows the upgrade progress for each component. The Database Upgrade Assistant writes detailed trace and log files and produces a complete HTML report for later reference. To enhance security, the Database Upgrade Assistant automatically locks new user accounts in the upgraded database. The Database Upgrade Assistant then proceeds to create new configuration files (parameter and listener files) in the new Oracle home.

Manual Upgrade
A manual upgrade consists of running SQL scripts and utilities from a command line to upgrade a database to the new Oracle Database release.

While a manual upgrade gives you finer control over the upgrade process, it is more susceptible to error if any of the upgrade or pre-upgrade steps are either not followed or are performed out of order.

When manually upgrading a database, you must perform the following pre-upgrade steps:
Analyze the database using the Pre-Upgrade Information Tool. The Upgrade Information Tool is a SQL script that ships with the new Oracle Database 10g release, and must be run in the environment of the database being upgraded.

The Upgrade Information Tool displays warnings about possible upgrade issues with the database. It also displays information about required initialization parameters for the new Oracle Database 10g release. Before starting up the new Oracle Database 10g release, make the necessary adjustments to the database.

1. Perform a backup of the database.

2. Add free space to any tablespaces in the database that require additional space, and drop and re-create any redo log files whose size is insufficient for the upgrade.

3. Adjust the parameter file for the upgrade, removing obsolete initialization parameters and adjusting initialization parameters that might cause upgrade problems.

4. Depending on the release of the database being upgraded, you may need to perform additional pre-upgrade steps.

After the Upgrade
View the status of the upgrade using the Post-Upgrade Status Tool. The Upgrade Status Tool is a SQL script that ships with the new Oracle Database 10g release, and must be run in the environment of the new Oracle Database 10g release.