Artstudio Pro app for Mac

I am unable to download the update 3.1, I get error message:

Unable to Download App

This app is on desktop and it is downloaded and I can open it up, but it will not update to new version w/all the updates.

I have contacted the App designer and they came back saying that the updating process is managed by the system, they cannot fix that in their app.

How do I get my app to update to the correct version?

Thanks,

April