Careful. If you remove the wrong drive, your VM will no longer boot. If you are worried, clone the VM first before proceeding.
# Power off the VM.
# <code>VirtualBox</code> → <code>click a VM</code> → <code>Settings</code> → <code>Storage</code> → <code>click on DVD device symbol</code> → <code>click on disk removal symbol</code>
# VirtualBox will ask
<blockquote>
Are you sure you want to delete the optical drive?
</blockquote>
<blockquote>
You will not be able to insert any optical disks or ISO images or install the Guest Additions without it!
</blockquote>
4. <code>click "Remove"</code>
