I love this tool on windows and online ,

1. How do you upload an aslx file saved by quest to the online version to resume editing it?
2. How you delete a published quest file?

1. You can't. You can download a file to edit it on the desktop version, but you can't upload it again.

2. You can't. But you can change its visibility so it doesn't show up on your profile, which is the next best thing. I believe the site administrators can delete a published game if you ask really nicely, but mostly I'd think there's no reason you'd need to.