In SQL Server Management Studio, try the following:
- Right-click database > Tasks > Backup...
- Check the box that say "Copy-only backup"
- On the left pane, select Backup Options and set backup compression to "Compress Backup"
With compression enabled, the database backup file should be much smaller than the original 500 GB. For reference, my 5GB database backed up with compression was 1 GB.
If you have nothing to lose, you can also try reducing the database log file size before proceeding with the backing up:
- Right-click database > Properties > Options
- Change database Recovery model from Full to Simple
- Right-click database > Task > Shrink > Files
- Select File Type Log and click OK
Hope this helps!