For web development I generally use either Coffee Cup Free HTML Editor or Notepad++, but sometimes good old notepad can be useful for typing up a simple meta redirect, ect if you don't want to boot either of those two programs, or whatever you use, up.
ok first you need to be able to edit the .html file
if you click on it now you will open your web browser and you will see what the lockscreen looks like, but you want it to open as a txt file so you can change it, right now the file is a .html, we want to change it to a .txt
so first thing is go start and search for folder options, open that and then click on the view tab, find were it says hide exstensions for known file types and uncheck it, now click apply.
next go to your .html file and right click it and click rename, just rename the .html to .txt and hit enter.
now your able to click on it and view the page source.
in the source you want to look for
<!-- Convert hours component of "12" to "24" --> //currentHours = ( currentHours > 12 ) ? currentHours - 12 : currentHours;
to change the time format to 12 hours just delete the two backslashs
to change your weather code first you need to find out what your weather code is. Theres different ways to do it so just google how to find your weather code.
now look for this in the .txt file
<!-- Weather Script -->
var locale = "xxxxxxxxx"
and all you need to do is copy your weather code into the quotations
now click save, exit and then rename the file back to .html and thats it,
i hope you understand all this as i am not a very good person to learn from, and i apologize for my 1st grade writing skills.
edit you may find it easier to just download an .html editor. instead of changing the .html to .txt.
i suggest coffee cup its free