You can follow these guidelines on how to download DS games on the web. These are just simple steps that you could follow but you can really find it helpful:

1. Connect your USB port on your computer correctly linking on your DS console.

2. Make sure that you have enough memory on your flash card so that when you transfer a DS game it would not be corrupted and you can have a successful upload.

3. Test the game first if it is running smoothly.

4. Scan the file with a reliable anti-virus to check if the file is completely clean.

These are just the few examples that you could follow.