Calibre is free. There is a Calibre forum here on Mobileread
https://www.mobileread.com/forums/forumdisplay.php?f=166. There are tips for using it and you can post any questions you have there. Calibre is very easy to use and does a great job converting .lit files. Here is the download link:
http://calibre-ebook.com/download. The developer is a member of Mobileread too.