That's mean they are in the workshop's folder.
You can find the 4K Blood Addon here: Steam\steamapps\workshop\content\4000\576560900
And the 4K Alien Blood Addon here: Steam\steamapps\workshop\content\4000\2181679625
You just have to go to your gmod's addons folder: Steam\steamapps\common\GarrysMod\garrysmod\addons
Create a folder with the name you want.
And just extract the two gmad files with gmad.exe: Steam\steamapps\common\GarrysMod\bin\gmad.exe
And put the extracted files in the folder you've created.
I'm really sorry if that's too complicated for you, I tried to make it as simple as possible.

how do i find 4k blood if the addon folder is empty but i have the 2 mods installed

Nevermind

What do you mean by that? If it's the size of the pool of blood, I can't do anything.

I did that but the blood is still big

Yes, that's right.

So I make a folder, and put both of them in?

You combine 4K Blood and 4K Alien Blood in the same folder in "Steam\steamapps\common\GarrysMod\garrysmod\addons\NameoftheFolder"

How do I do this?

and how will I understand where the "4k alien blood" addons are located in the folder?