If you have both tables sorted by account number, then you could also perform a DATA MERGE between the two tables, being the smaller one on the right side of the MERGE statement (to overwrite values of the left side table).
I have a change in plans. So I have the dataset with 2 million records give or take. I then have a smaller dataset of about 2000 records. Both have the same variables and names. Once again the main variable I am using is accountnumber. Of the 2000 records in the smaller dataset, there are about 1500 of those same account numbers in the larger dataset. Only the account numbers would be the same, with the rest of the data on that line being different. I need to tell SAS to delete the entries in larger file that have matching account numbers in the smaller file. So, 1500 or so records would be deleted from the larger file that have matching account numbers in the smaller file. Is this possible?