Yes. You can change to any plan you like anytime. You will be prorated, meaning you will only be charged the remaining amount (if any) for the rest of your billing period.
For example, you can start with a monthly plan paying $20/month, try out the platform, and if you like what you see and it fits your workflow, just change your plan to the yearly plan and enjoy a 50% discount (since the yearly plan is only $10/month).