Changing a page’s title in a Bootstrap theme

I'm a beginner in HTML/CSS and was using this Bootstrap theme for making my personal website. As you can see, the nav bar has Top, Work, Portfolio and Contact. I want to rename Top as About. For that, I replaced Top by About wherever necessary in index.html but the result isn't what I desire. The website gets messed up with the About being an inactive link. Should I change the CSS files and do the replacement there as well?