I would first ask, why? The only time you should store numbers as numbers is if you are going to be performing calculations on them. For instance, Social Security Numbers, Zip Codes, Phone Numbers are all numeric, but you don't add any of them together. If you don't do any mathematical calculations with these numbers, don't change them.
If I decided for some reason to do it anyway, I would BACKUP the database. Then I would create a new field in the table as the datatype you need. Then do an update query setting the new field = to the old field (you may have to convert the datatype in the query to get it to work, may not). Once you check that the information in the new field is correct, remove the old field.
Not sure if you will run into any issues with queries though by changing the datatype. I know that my front end would CHOKE if I changed something from a string to a number.
Leslie
