1. Download or install a clean WotLK 3.3.5a client.
2. Download the Sunset WoW custom patch/launcher files from the Downloads page.
3. Open your WoW folder.
4. Go to:
Data/enUS/realmlist.wtf or Data/enGB/realmlist.wtf
5. Replace the file content with:
set realmlist sunset-wow.org
6. Save the file.
7. Start the game with the Sunset WoW launcher if provided.
8. Log in with your account.
9. Create your character and start at level 80.
If you cannot connect, open a support ticket.