If you can't understand how to do it and at the same time you don't have money to buy it, you can freely compile the source code and use the program for as long as you want.
LINKS:
http://www.aseprite.org
https://github.com/aseprite/aseprite/
https://github.com/aseprite/aseprite/...
https://github.com/aseprite/aseprite/...
http://www.cmake.org/
https://ninja-build.org/
COMMANDS:
cmake -G Ninja ..
ninja aseprite