Change html page template to existing home page of php website

I have a website that needs a new home page. I want to use an html template that I have for the new home page. I attached a screen shot image of how the website home page currently looks and how it should look when the html template is added. Also, notice on the screen shot, the bottom new home page, there is a second navigation (welcome, how it works, who its for, free vs paid, examples, for dummies) . I want this navigation to have certain links on the guest home page and different links when a member is logged into the website. Would also need the blue sign in button to open the login form and the green join button to open the registration form. Project recap 1- implement html theme to home page of site with no compatibility problems. 2- the second navigation needs to show different links when user logs in to member home page. (second navigation is on the bottom homepage on screen shot - welcome, how it works, who its for, free vs paid, examples, for dummies) 3- Make it so a user can click the big blue sign in button to open login form and big green join button to open the registration pop up form. My website uses php/css/html/jquery/javascript/ajax , so theme needs to not have any conflicts.