First of All,you will need the tool "HLM Wad Explorer" which can be downloaded here[github.com].

Ok,time to Start,probably you wanna try to change a Playable character first,so let's do it
Open the HLM Wad Explorer and find you Character,in this case,i'm gonna edit the biker sprites
so,let's do it:


you need to pick ONLY png files,meta files is just configuration files(which you can't edit)
all the Playable characters have the prefix "Player_" on their names,so the biker one is "Player_Biker.png",click on Resource and then Extract to extract the Sprite:


Warning: You first need to click on the Player Sprite(it will be Highlighted with a Blue Color) and THEN extract it

Ok,now you need to edit the .png file you extracted
to do it you will need a Photo/Sprite editing program,i will use Game Maker 8 which have a Internal Sprite Editor

Obs: Don't Use Paint,you will need a Image with no background,paint will add a White background to the Image

i'm gonna edit only the Color,you can edit Anything you want,but you can't do these things:

• Change the Sprite's Width or Height (Resolution)
  
• Add a Background (Like the White Ones that Paint add)

Just it,ok you Edited the Sprite:



then you save it on any folder and go to the HLM Wad Explorer,then you need to find the sprite again and click on it,then you click on Resource and then Replace,find the png image and open it:



it will change the Sprite name on the editor to a Bold one
and the results will appear on the screen:



Now you can Save it on File >> Save as
put on any folder and name it with the Level/Campaign name

ok,you already created the .patchwad with the custom sprites,now you can put it on your Levels/Campaigns,but how? Let's See

First of all you need to put the ".patchwad" file you made on the Hotline Miami 2 mods folder which can be found here:

• Windows: Documents\My Games\HotlineMiami2\Mods
  
• Linux: ~/HotlineMiami2/Mods (SteamOS too)
  
• Mac: ~/HotlineMiami2/Mods

Put the Patchwad file there and close it
Ok,now you need to create your Levels/Campaigns,just make them,you don't need to do anything special on Hotline Miami 2,the Custom Sprites will be already loaded.
Here at Steam you can find Pretty Good guides teaching how to make Levels,Cutscenes and Campaigns.

Now that you've already made the Levels/Campaigns you need to go to the Editor on Hotline Miami 2 and Highlight the Level(just select him),then you need to Press "O" and it will open the Level's/Campaign's Folder,Create a new Folder called "mods' and put the Patchwad file in there.

Ok,now you will need to create a .zip with everything inside the Level/Campaign folder

Now you have your Level with the Custom Sprites :v you can Put it on Reddit and other sites and the custom sprites will be loaded.

Final Result:


Thanks to Everyone and sorry for English Problems,i'm from Brazil and it's my first Guide too :v
Goodbye