Complex sentence: Since version 5.0, FrostWire relaunched itself as a BitTorrent application, so those using the Gnutella network either have to use version 4, or switch to another client, altogether.
Split into simpler sentences: Since version 5.0, FrostWire relaunched itself as a BitTorrent application. After version 5, FrostWire can only download torrents, so those using the Gnutella network either have to use version 4, or switch to another client, altogether.