First download the Oracle Apex 5.x from the Oracle.com with the following link:
Then start the sqlplus and give the SYS credintials to logon as following:
SQL*Plus: Release 126.96.36.199.0 Production on Thu Aug 27 16:36:43 2015
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SQL> connect SYS AS SYSDBA
After connected run the following script as given in the example below:
SQL> @apexins.sql SYSAUX SYSAUX TEMP /i/
SQL> @apex_epg_config.sql /software -- this is the folder in which you extracted the zip file.
Up-gradation is complete and now you can run the Apex 5 successfully.