This tutorial shows how change form validation messages in Drupal 7.x.
Once you submit the form without filling in all the required fields, you get the error message that field is required.
In order to change the form validation messages, you should do the following:
Log into your hosting cPanel or ftp.
Locate sites/all/themes/themeXXX/js folder.
Open jquery.loader.js file to edit:
Locate Contact form tooltips section of the code and modify the messages:
Save changes in the file.
Feel free to check the detailed video tutorial below: