I'd recommend read wpForo Documentation. It has many options and settings you should know to manage it well. All settings are located in Dashboard > Forums > Settings admin page Tab.

The answer on your question can be found here:

https://wpforo.com/docs/root/wpforo-settings/features/

Just disable the "Show Top/Menu Bar" option.

Complete novice to website design, so I'd really appreciate your help.

I want to get rid of the whole grey menu bar at the top of the page, including the search icon to the right of the menu bar. So far, as my background colour is white, I've managed to change the colour of the menu bar (#3) to white also tomato it  become invisible, but it hasn't gotten rid of the search icon to the right of the menu bar.

Two questions:

1) Is there a way of getting rid of the whole menu bar including the search icon?
2) if not, how do I get rid of the search icon in the menu bar?    

Many thanks