I have this sprites in Unity and I want to join a head to a body and a gun but I only find tutorials on how to splice. How can I do it?
Create an empty game object and make your sprites children of that game object.
So like this:
GameObject (Parent)
Head
Gun
Body
If you want to edit the sprite itself, you can use photo editing programs like Photoshop or Aseprite. If you don't have those, you can use Photopea