Many Mexicans, especially those that work in the tourism industry, speak English.  You do not need to know how to speak Spanish to get by.

If you’re planning on staying for an extended bit, its wise to learn a little bit of conversational Spanish – you will find that Mexicans will welcome and help you speak the language.  If you do speak, even only a little Spanish, give it a try while you’re here – don’t be shy – and you’ll enjoy the experience even more so!