I am writing a paper that needs to be formatted using the LNCS style, which is not available out of the box with LyX 2.2.3. How do I install it on my LyX install for Windows 10 x64?
Step 0: Quit LyX
Download llncs2e.zip, which contains llncs.cls and llncsdoc.sty. I just googled for a download link and got mine from here
Copy those files to the folder ... \ MiKTeX 2.7 \ tex \ latex \ lncs, where ... \ MiKTeX 2.7 is the folder in which MiKTeX is installed. On some systems, copy to ... \ MiKTeX 2.7 \ texmf \ latex \ lncs. The lncs folder will probably need to be created.
Mine was in
C:\Program Files (x86)\MiKTeX 2.9\tex\latex, where I had to create the
lncs folder (which requires admin privilege escalation). I extracted
llncsdoc.sty to this folder.
Run "texhash" from the command line.
cmd and run
texhash. Very straightforward
Run MikTex Settings. Press "Refresh FNDB" under General. Then, possibly, "Update Formats".
It wasn't obvious to me where MikTeX Settings was. This other SX post showed me what to do. Just look for
admin in the Start Menu's search bar and you'll see
MikTeX Settings (Admin)
Open Lyx and select Tools -> Reconfigure
You're done. Go do a happy dance or something
I'm using MikTex 2.9 on Windows10 and I didn't get the MikTex Settings by searching for it in the start menu. Instead I found it in the MikTex Console - run as admin, go to "Tasks" on the menu bar and run "refresh file name database". Took me some time to realize FNDB stood for "file name database"...
The previous answer is a very good answer, and I still got stuck on step 4 - if I skipped step 4 the document class just wouldn't become available. I would like to put it here in case someone else stumbles across it. Sorry for not being able to add a comment, I don't have enough reputation here.