just copy the file to the folder exp/stan/nmr/au/user in the topspin directory. Or do "edau", the change to the user folder with the source selector in the upper right hand corner. Then use "Import" in the File menu and import the file from its current location.
What Dr. Anklin said. Also is it a macro or an au program? If it's a macro you can also type 'edmac' in Topspin, then click Edit to copy into an existing macro, and then 'save as' the new one.