You can save your sprite using the File > Save menu or pressing Ctrl+S (⌘S on macOS).
We highly recommend you to save your sprites in the
.aseprite format, so you keep the full sprite
information intact (layers, frames,
etc.). But you can save your sprite as other file types if you don't
need all this information. For example, you can open a
.png file, editing it, and save it again as .png (without using
the .aseprite format).
If you want to export your sprite as a .png file or a .gif
animation, you can use the File > Export option. See the
Exporting section for more information.
SEE ALSO