Honestly you are better off talking direct to the program creator, EricLang (member of this forum). However since he isnt online much anymore it may require help from multiple members here to get into. Ill guide you in the right direction, even try to solve some problems if I know how to fix them
First thing to do is to get the program from its website:
http://home.hccnet.nl/ericenzwaan/lemmix/lemmix.htmYou will see a link showing "Download Lemmix Level Editor latest alpha version" This should be self explanitory
Now it is reccommended to keep scrolling down past that link after downloading to have a look at the information on Mouse usage, Controls and basics on making a level. It also helps to examine the two screenshots of the program at the bottom
On to re-creating your levels. If you know which graphics set and which game they came from (whether it be the original lemmings, oh no more lemmings, holiday lemmings,etc) then this will make it easier.
Although it is possible to combine graphics sets of different games like I did, it would be reccomended to use just one set of graphics sets. As far as I know the graphics files do not come with Lemmix and you will need to find them yourself, or get one of us to send them to you.
I'm nearly falling asleep with so much of this typing, lol, so I think ill end it for now. Any further help you need just ask us