Current Setup :

Apex Version : Oracle Apex 5.0
Webserver : ORDS Running on Apache Tomcat 9
DB Version : Oracle 12.2 

• Step 1: Download Apex 18.1 from Oracle Website
• Step 2: Rename the old apex directory in ORACLE_HOME

cd $ORACLE_HOME
mv apex/ apex_old/

• Step 3: Unzip new downloaded apex software and go to the new Apex Directory and run the Upgrade

cd apex/
SQL> @apexins.sql apex apex temp /i/

• If you are using Embedded PL/SQL Gateway to access Apex application, perform below steps: 

Load Images Directory for Apex.

@apex_epg_config.sql ORACLE_HOME

@apex_epg_config.sql /u01/app/oracle/product/12.2.0/dbhome_1

• If you are using ORDS to access Apex application, perform below steps: 

As tomcat user
cd /u01/app/oracle/product/12.2.0/dbhome_1/apex/images/
cp -R * $CATALINA_HOME/webapps/i
sh $CATALINA_HOME/bin/shutdown.sh
sh $CATALINA_HOME/bin/startup.sh

• Step 4: verify Upgrade 

SQL> select VERSION_NO from apex_release;
VERSION_NO
--------------------------------------------------------------------------------
18.1.0.00.45