Generally you can try to copy files with extension .CFG from your previous installation to the new one, but be careful with file MIME.CFG, as new one can describe DGI applications required by the new installation of Arachne. You would probably also like to use your old bookmarks - HOTLIST.HTM file. Files in MAIL subdirectory can be simply moved to the new mail directory, or you can use common mail directory or all installations of Arachne on youe PC.
In future versions of Arachne, there will be added user friendly way to upgrade.