Here’s a quick review of the (assuming you’re referring to a skin with “64” in the name or a skin designed with a 64x64 resolution, which is the standard for modern Minecraft Java and Bedrock skins).
For precise control, use programs like Paint.net or Photoshop. Just ensure you save the file as a transparent PNG at exactly 64x64 pixels.
(average – fine for basic use, but not memorable unless the design is creative)