Navigation Bar Help!?

Originally my navigation bar was aligned to the left but I wanted the buttons spread out evenly. Someone managed to sort this out for me but this was nearly a year ago.

I now would like to add a page or two to my navigation bar but I’m unsure how as the code has been changed and it’s now not a case of just publishing a page and it appearing.

I’d really appreciate some help.

My site is: https://www.sunderlandfootball.co.uk