There are 2 ways that you can rename your menu

Step #1:

Sometimes you write a Page/Post with a long tail keyword. For example, "Wealthy Affiliate review - the best online university."

If you put this Page/Post to your menu, it doesn't make sense to have such a long menu title. Then you want to shorten the title. But what is the solution?

When you put a Page/Post as one of your menu items, you can rename title via Quick Edit that I described in last pages. But if you rename it by changing the title, you're going to change your Keyword. We don't want to change the keyword.

Then You can rename your menu without changing the keyword.

Step #2:

Go to Dashboard -> move your mouse on Appearance -> Choose Menu

Then Choose which Page/Post you want, then add it to a menu. In this case, I add "The Wealthy Affiliate reviews 2017 best affiliate university"

As I showed below, Click on the Page arrow to expand it.

Now you should change NAVIGATION LABEL. You can rename it to what you want.

Then, SAVE menu and finish. You rename your Page/Post without changing your main title and keyword.