Once you upgrade Application Express within your Oracle Database XE, you will lose the Oracle APEX interface to perform some of your database management functions. This includes the ability to create and alter users, set database parameters, etc. To perform these functions, you will need to use either SQL Developer or SQL*Plus.
The following is a list of database management functions that cannot be performed in later versions of Application Express but that were features of Oracle APEX 2.1, the default interface of Oracle Database XE. For each, there is a SQL Statement provided that can be executed either in a SQL Worksheet of Oracle SQL Developer or using SQL*Plus when connected to your Oracle Database XE. Most of these commands need to be executed as the user SYS.
For more information about Oracle Database XE, visit the Oracle Database 10 g Express Edition OTN site. Please note that this Application Express upgrade does not change the support policy of Oracle Support. Oracle Database XE is supported only via the OTN forums. Oracle Support will not answer questions about any Application Express on Oracle XE issues, installation or otherwise.