First what you gotta do is download a program called slab6 found here ---> http://advsys.net/ken/slab6.zip
Then extract slab6.exe to where you installed Ace of Spades.
Double click any .kv6 file and select "open with program from local disk" or whatever it says.
Navigate to where slab6 is, which if you've been following this tutorial, then it should be in C:/Ace of Spades and then double click slab6.exe.
BEFORE YOU HIT OKAY
There is a checkbox to the left, that says "Always use the selected program to open this kind of file." Click the box so it
has a checkmark.
THEN HIT OK
Now when you try to open a .kv6 file by double clicking it, you'll be able to edit it.
CONGRATS.