With almost every patch or release upgrade of the Oracle Database a new version of Oracle Application Express (APEX) will be installed. And as APEX is part of the database installation it will be upgraded as part of the component upgrades after the ORACLE SERVER component has been successfully upgraded to the new releases.

But the APEX upgrade can take a bit (several minutes or even more in some cases). Therefore it is a common advice to upgrade APEX upfront before upgrading the database as this can be done online while the database is in production (unless your databases serves just as an APEX application backend - in this case upgrading APEX upfront won't save you anything).

To upgrade Oracle APEX upfront you'll have to follow
MOS Note:1088970.1.

It explains that you'll have to:

1. Determine the installation type by running this query:
   select count(*) from <SCHEMA>.WWV_FLOWS where id = 4000;
   whereas <SCHEMA> can be one of the following:
   FLOWS_010500 1.5.X 
   FLOWS_010600 1.6.X 
   FLOWS_020000 2.0.X 
   FLOWS_020100 2.1.X 
   FLOWS_020200 2.2.X 
   FLOWS_030000 3.0.X 
   FLOWS_030100 3.1.X  
   APEX_030200 3.2.X 
   APEX_040000 4.0.X
   APEX_040100 4.1.X
   APEX_040200 4.2.X
   If the query returns 0 then you'll need to run apxrtins.sql
   If the query returns 1 then you'll need to execute apexins.sql
   
   
2. Download the newest APEX package and install it.