DiskSlim – Disk Cleanup Pro 12.1.6

Mount the image, drag the app into the "Applications" folder and launch it. If the system blocks the launch, allow it in "System Settings → Privacy & Security".

Reinstalling from a fresh image usually helps. Make sure your macOS version matches the one listed in the compatibility specs.

Download the new version from the site and install it over the current one — your settings will be preserved.

Try a mirror or a download manager. For large files the browser often drops the connection.

Use an uninstaller utility — it cleans up the service files that remain after moving the app to the trash.