In order to delete the chat history in Softros LAN Messenger you can try to open your program -> right click on a contact -> press the 'View User History' and a new window should appear -> press the second button on the right corner 'Browse log files' and a new window will open. Open the Messages.txt file, select and delete the lines that you want or simply delete the file (this will delete all your history). Don't forget to Save before you close the document.