Go to the website: https://admin.mt4professional.com/

In the upper right-hand corner, is a "Gear" with a pulldown menu... select "Your Settings". 

Then on that page, on the Left menu is a Billing "Subscription" link... 

Click that, and in the upper right-hand corner is a RED "Unsubscribe" button. 

Click it to cancel your automatic payments and trial.

Once you do that, your plan will automatically end. If you are within the 14-day free trial period the plan will end after 14-days from the day you started and you will not be charged. Otherwise, the plan will end on the expiration of the billing month, and there will be no more charges.