Changing database field to accept alphanumeric value


I have an application developed withh Yii (not by me, not a coder), which has a database field which as of now accepts only numerical values, and I need to change it so that I can insert alphanumerical values.

By looking at the files I am guessing that I need to edit the files in the models directory, am I right, if so is it possible to post the code here for your assistance?

Thank you