First of all; take a backup copy of your current installation!
Both the directory in the Tomcat webapp and the database!
Unzip the vp_installed_2_4_2_upgrade_from_2_4.zip anywhere on your disk
Start to update your VisionProject database by running the SQL script 'upgrade_from_2.4_to_2.4.2.sql' located in the directory: '\WEB-INF\internal_docs\installed version\db_scripts\v2.4.2\Upgrade_from_2.4'.
Take a copy of the file web-inf\struts-config.xml.
Delete all *.jar from the web-inf\lib directory
Then you can copy your unzipped files from 1. into your VisionProject webapp.
A new struts-config.xml has now been copied into your VisionProject installation and you now need to change the database properties to the ones you had originally.