Excel Macro for matching and updating quantity

We are using a barcode scanner to do an inventory in our stores. We will scan every item UPC code and it writes it to a txt file on the device. If we have 2 of the same item it will write UPC twice in the text file etc... I plan to copy the txt file contents to a column in the same inventory spreadsheet we will be working with called SCANNED UPCS. In the inventory spreadsheet I have all the existing product UPC codes in one column (UPCS), and descriptions and style codes in other columns - I also have a quantity column for each product called QUANTITY. I need an excel macro made that will update QUANTITY for each item based on if the UPC code is present in the SCANNED UPCS column. If there are 2 or more of the same UPC code present in the SCANNED UPCS column - it needs to make the quantity for that item 2 etc.. Also please make note in Macro where I can change the column location where it targets and writes to please.