If there is only one
var cadena = "I´m from Mexico".replace('`', '');
To replace all occurrences, use regular expressions:
var cadena = "I´m from Mexico".replace(/`/g, '');
See the JavaScript String.replace method https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/replace
solved How to delete or replace ´ in JavaScript? [duplicate]