There are a number of ways of dropping to four stats, in my experience. Remember that if you're going to make something a stat, you're asserting that that quality is going to have a very specific place in your game.
--It has to govern something important and commonplace enough that it's worth the space of your sheet and having a low number is a real handicap.
--It has to govern something limited and specific enough that other stats still get used and you can't get by on it alone.
--It has to govern something that it is okay for characters to be very good or very bad at.
So let's look at the Apocalypse World stats.
Cool is an interesting stat because it doesn't represent a specific field of endeavor, but is kind of a catchall for things which aren't explicitly covered by another stat. As such, there are a couple of ways you could get rid of it.
--Act Under Fire is always 50/50. Basically, everyone has Cool 0.
--Everything is governed by a stat. When you Act Under Fire, the MC determines the category the fire comes from and you roll that. Suppose that your stats were something like "Assassin, Spy, Saboteur, Cultist." If you were acting under literal fire to make your escape, you would roll Assassin. If you were acting under fire to resist manipulation, you would roll Spy. If you were acting under fire to repair your plane's engine before it crashed, you would roll Saboteur.
Weird can only exist as a stat if the magic level stays very near what Apocalypse world has. Either more or less magic means no Weird.
--In a "mundane" setting, you could simply strip out Weird and run on Cool/Hard/Sharp/Weird.
--In a more magical setting, Weird gets split up. You could run a Potter game where the stats were Charms, Potions, Dark Arts, and Courage
Hot assumes that the same characters are good in all social situations.
--If socializing is very important to your game, you could make every stat social. Roll with, say, "Street, Suit, Uniform, Fashion." Each stat makes you good at talking to people who dress that way *and* doing things you'd expect people dressed that way to do. So to build a computer, you roll Suit and to shoot a dude in the face, you roll Uniform.
--If it's not important, you could do the same thing. (Every NPC is either cool, hard, sharp, or weird. Roll the appropriate stat to manipulate them). Or, just let Cool absorb Hot's functions entirely.
SharpGives some--and only some--characters the right to ask questions.
--If you don't like the questions mechanic, just axe the stat.
--If you want everyone in on the action, let each stat provide information about related topics.
Finally, Hard assumes that some characters can be bad at fighting, and how you fight doesn't matter. If you were designing a game about soldiers or ninjas or martial arts masters or something, you wouldn't want "hard." You'd want each stat to be associated with a fighting style.
For a fantasy adventure game your stats are Bushido, Ninjutsu, Maho, and Ki. Each one can be used to seize things by force, but they provide different side benefits.