First of all head to Learn With Kentico portal, all cources are there. To prepare for the exam the best course is Online Marketing Essentials (v12). When you complete the course you will receive a voucher for the exam. Alternatively, you can buy voucher here.
If your organisation is a Kentico partner or you have a valid Kentico license with maintainance you can get one or more of Kentico courses for free, please contact Kentico via email to find out more.
From my experience I'd suggest at very least complete the course and have some practice on more or less live project before taking the exam.