gitPDFtoPNG is managed using git. The repository is available from gitlab.
You can fetch it with:
git clone git://gitlab.com/zerodogg/pdftopng.git
Then you can
git pullwhenever you want to fetch the latest changes.
If you want to make changes to the code you can fork it on gitlab (as long as you have a gitlab account - if you don't it's gratis to make one), remember to issue a pull request if you want your changes included upstream.
The reposity can also be viewed with the gitlab web UI.
If you need information about how to use git, have a look at http://progit.org/.