Hello - Could use a bit of help, please.

I'm updating my 2017 website which I did with Xara - www.IGCChicago.com . I'm hoping to correct a construction error I made. All my top menus are independent to themselves, so if I need to make what should be an 'universal' change on all menus, on all pages, unfortunately .... I have to do them individually. Quite time consuming. Now, I did (perhaps a bad beginners error) create each 'page' as a separate page (really in Xara terms, a separate 'website.') So ..... to make a long question short, is there any way of tying all my 'separate' menus together - given the way I have things built? By the way, the reason - in my thinking - that I did not do all 'pages' as part of one website is that the file would incredibly too large to working with, perhaps upload to my server, etc. Can you give me some enlightenment on this problem, please? Could I have gone about building my site in better manner? - If so, kindly advise in what way? Thanks so much - Jeff