If something comes up and you can no longer make the time you scheduled your exam for, you always have the option to cancel your exam for the time being.
On RegisterBlast, locate the History section and find the test you need to make changes to. Click "Cancel" to begin the process.
You will be brought to a page that asks you to confirm your cancellation, If you cancel, you'll have to re-register for your exam, assuming any time slots are still available.
Click "YES, CANCEL MY REGISTRATION" to confirm your selection.
With your cancellation complete, your account history will no longer show the exam you chose to cancel.