batch update in MS Access

Here is my situation:

I have two MS Access 2010 tables in the same database. There is a UPC code in both table A and table B.  Table A contains an ingredients column with data in it.  I need to access the data in Table A and then find the same UPC code in table B and update the Ingredients field in it. Table A contains several thousand records, so this query needs to be able to loop.

Any ideas?

I need to know how to run this update inside MS Access (using the tools in it)

Thanks!