Yes, we offer monthly plans as well.
To upgrade to a monthly plan,
Go to the pricing page
Change the switch to "Monthly" (click here to see how to do that)
Click "Buy Now"
Note that monthly plans don't include the 7 days trial, only yearly ones do.
In monthly plans you are charged every month for the monthly fee. At any time you can downgrade from the account settings. You will only be charged for the months you used the service, last month being the one that started before you requested to be downgraded.