How to access additional fields when manually upgrading a listing

Have a situation where we want to upgrade some free listings to a paid listing but without requiring any payment. I went into the places listing and changed over on the right the selection from free to standard (paid). We want to make additional fields available for display on paid listings and the packages are defined as such, however I don’t see how I can get at the additional fields when the ad was first input as a free ad. Is there a way to change a place listing from free to standard and get access to those fields to add the additional data in that we allow for standard paid listings? Thanks