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_1upgrade_from_2_4.zip anywhere on your disk
Start to update your VisionFlow database by running the SQL scripts included in the directory: '\WEB-INF\internal_docs\installed version\db_scripts\v2.4.1\Upgrade_from_2_4', from 01. ProjectSystemUserJoin_new_column.sql to 05. ProjectSystemUserJoin_Update.sql.
Take a copy of the file web-inf\struts-config.xml.
Then you can copy your unzipped files from 1. into your VisionFlow webapp.
A new struts-config.xml has now been copied into your VisionFlow installation and you now need to change the database properties to the ones you had originally.