First, make sure you have the latest version. In the "Benchmark" dialog there's a checkbox at the bottom left which says "Upload Results to Leaderboard'. If you are using the High, Extreme, or Crazy presets your result will appear in the corresponding leaderboard.

To view the information click on "Multiplayer", "Rankings", and "Benchmark". You should see your system details listed and the benchmark scores for the various presets are below as a card (which you can click on!).

NOTE: If you submit any benchmark result (but not a preset) your system information will still be listed but you won't appear in a leaderboard.