Yes you can change you plan anytime.
You will be billed with new pricing after the purchased time period has ended.
- Monthly to Yearly: For example, if you are on a monthly plan, and you decide to change to Yearly plan in June 2016. Then you will billed with Yearly pricing from Jul 2016 to Jul 2017.
- Yearly to Monthly: You can change your plan to monthly plan. Once your yearly plan is over. Your monthly plan will start.
Do you still need clarification or help in regards to this ? Please send an email to email@example.com and one of our friendly staff will be glad to help you.