There are a couple of ways to do what you want.
If you have Client Access “Personal Communications iSeries Access for Windows”, there is a button on the tool bar to upload files. You’ll need an FDF which is easy to get if you download the file first using the bottom on the tool bar to download files. Proceed with caution.
Another way is with the VBA in Excel and the Client Access ODBC driver.
Quick and dirty updates aren’t that tough, but if you want to make sure users don’t enter the wrong thing in the wrong place, it gets more complicated – too complicated for this forum.
If you want a template for updating AS/400 files from Excel, e-mail me and I’ll send you one. I intend to make this sort of thing a future topic in my blog: Beyond Excel.