Correcting a shipping entry mistake?

I'm just in the process of rolling out FA for a new small business and I'm entering records into the system to match what we did on paper in the first week of business, before I had FA ready to go, but I've run into a problem.

We use three storage locations - a main warehouse and then two staging locations for handling small orders. One of those staging areas sold a handful of product last week, and yesterday I went in and recorded all the transactions. Unfortunately, I forgot to change the "ship from" location on the delivery form, so I now have a inventory mismatch, showing more items in my staging area than are really there, and too few in my main warehouse, which is the default setting for "ship from". I have already dispatched the deliveries with this erroneous info, and posted the invoices.

Is there a way that I can edit the delivery records to change where the inventory came from, or am I out of luck on the easy fix, since things have now been posted? And assuming I have to do things the hard way, which way would be best? Transfer a corresponding amount of stock from the staging area back to the main warehouse? Some kind of GL correction? I'm a complete newbie when it comes to formal accounting, so any advice would be appreciated.

J