First, you can now perform this routine by selecting the name you want to delete in Names File Maintenance and selecting Routines > Delete and Merge Name. In AM4, you have to select Options > Names > Special Routines > Merge Two Names.
Second, the user interface for selecting which information will remain in the merged record in substantially different from AM4. In AM4 you select the Keep checkbox if you want to keep the old value, otherwise, the system uses the new value—the value of the record you are merging into.

AM.NET approaches this a bit differently.

AM.NET now clearly shows which values will be used in the Merge Result column. To change the value, simply click the green arrow. This disables the arrow from the other record, and allows you to easily see which values are being used for which fields.
When you are confident
that the data is correct, click OK. AM.NET will merge all linked records (event
registrations, dues information, etc.), to the merged record.