If, for security or other reasons, you want to disable the download button on your assets, as shown below, you can do this in your account settings.
First, click on your account name in the top-right corner, then select "Preferences" from the drop-down menu or navigate to the preference settings page.
Next, check the box titled: "Disable ability for user to download content from management portal." and click Save.
Now, users are no longer able to download assets from your account!