need help adding fields to Client

I'm fairly new to ProjectPier, and trying to adapt it to my purposes of tracking technical sales projects with a small group across the US. Our customers all have an account number associated with them, and I would like to add that to a project for each customer we are working with. I would prefer not using a predefined field like FAX for this, it would be better to add the field I need to the database.
thanks,
mike