Enfold theme – menus and links

I used to have wordpress.com blog and have now moved over to the .org. I do not have a proper main menu and sub-menu set up. I have been looking at themes to buy and am thinking about going with with Enfold. Some of my webpages have high google rankings but the url looks messy and isn’t part of a menu. I am worried that if I buy the theme and then put in proper menus with sub-menus then I would need to change the current high ranking url and potentially lose my high google ranking as google won’t find the link to that page again as I would have moved it under a sub-heading. How to tackle this?