Use fewer for things that can be counted:
...fewer seats...
...fewer problems...
...fewer cars...
Use less for things that cannot be counted:
...less vitality...
...less meat...
...less truth...
Words like "space" and "room" and many others could go either way, depending upon the intended meaning.
...There were fewer spaces to park after the renovation.
...There was less space between the seats after the renovation.
...I counted fewer rooms available this year.
...I had less room for my luggage.
Happy punctuating!
Margie