If you've registered to take an exam with Pearson VUE, you have the options to reschedule for $50 or cancel for $100.
Part of the rescheduling policy is that the exam must be taken with 365 days (I presume from the date for which the exam was originally scheduled) or you will forfeit your exam fee.
If you feel you won't be ready within 365 days then you should just cancel rather than reschedule.