We strongly urge you to take a backup of your data first, before proceeding with any of the following functions!
There are a number of function in phpMyAdmin for managing fields within your database(s). The below videos will walk you through the various steps.
Insert Field
This video will demonstrate how you can insert fields into your database tables using phpMyAdmin:
Modify Existing Fields
The next video will show you how you can modify existing fields:
Delete Fields
If you want to fully delete a field, simply follow the steps in the next video: