… also (see above), why does it say “Track” and “Rack” between channels 3 and 4? This seems very random! I’d love to be able to delete them though, been trying for 2 months to get rid of them, I wish I didn’t need to upgrade from my perfectly good Cubase 6 
Hope someone can help!
To answer your first question, it should disappear as it does on my system when I select “No Instrument”. Not sure why it doesn’t on yours. What OS?
Track and Rack instruments are different, if you have both listed you must have created both or chosen/imported a template with both on. There are plenty of discussions here on the forum over which is “better”. Personally I mainly use “Track” instruments but don’t want to bog you down in a list of all the differences and personal bias between one of the other.
There are a lot of changes since 6 but once you’re used to it I think you’ll like most of them. I moved from 6 to 8 a couple of years ago.
In the ‘Track’ section of the rack, the ‘No VST Instrument’ slot will remain for as along as the associated VST instrument track exists in the project. If you wanted to get rid of the empty rack slot you’d have to remove the VST instrument track from the project.
Why is it like this? You may want to set the rack to ‘No VST instrument’ for a VST instrument track but keep the data on that track.
If, however, you select ‘No VST Instrument’ in the ‘Rack’ section of the rack, the slot for the VST instrument will be removed completely.
For an explanation of the difference between ‘Track’ and ‘Rack’ please see the manual.
I am having the exact same issue. I on a PC using Cubase 9 and I cannot remove a VST instrument once it is added to the rack. “No VST Instrument” does not remove anything. A simple X button would go a long way. Cubase I think we are due for an update please.
Thanks
I had the same problem, drove me nuts. Finally I figured it out and it was so obvious that I kicked myself. Then I forgot all about it and had the exact same thing happen all over again.
Click here instead of the arrow on the side:
Select “No instrument”.
A clickable area should be marked in one way or another. In the earlier days of Cubase we had 3D buttons so that we knew where to push. In today’s GUIs it’s out of fashion I’m afraid.
----> Necromorbus
Thanks a lot for your advice.
I clicked the arrow 10 Billion times - who would think you have to click the name of the instrument.
A down arrow beside a name indicates a drop down list. Steinberg should really stick to the conventions.
Many people don’t explain things very well. You have to click on the instrument name. If you want to remove HSO from the rack, click on “HSO”’ printed right on the front panel of the HSO instrument. It looks like a label but it is actually an active part of the screen. In other words, when you click on it, something happens. It’s impossible to tell that it is not just text. What will happen is a list of your instruments will drop down. Choose “no instrument.” HSO disappears.
Thank you for sharing this. Spent ages trying to do it.
Thanks for sharing…
Me too have been spending time clicking away trying to working out how to delete a instrument from the VST rack.
Steinberg developers, There must be an easy way of implemented a delete, click X raise a dialog box ask the question about removing the VST and its track from the project. 
Indiscriminately removing an Instrument Track from the rack would be a bad accident waiting to happen. Just remove the track itself using the track list so you know what you’re removing. This will also remove the plugin.