Summarize the following:
Even though the words differ, you should still sing the Italian "happy birthday" song to the tune of the "happy birthday" song you likely learned in English. The most commonly used lyrics for the "happy birthday" song don't actually mention birthdays at all. Instead, you're using the indirect "best wishes" expression in place of "happy birthday" in the standard tune.  You'll follow the expression with "a te" (ah tee), meaning "to you." The song lyrics are: Tanti auguri a te, Tanti auguri a te, Tanti auguri a (NAME), Tanti auguri a te! While it isn't used quite as often, you can technically use the direct "happy birthday" expression in place of the English expression in the standard song.  As with the "tanti auguri" version, you'll need to follow the phrase with "a te" (ah tee), meaning "to you." In this version, the lyrics are: Buon compleanno a te, Buon compleanno a te, Buon compleanno a (NAME), Buon compleanno a te!

Summary:
Use the familiar tune. Sing "tanti auguri" for several lines. Consider switching to "buon compleanno" instead.