This is a no risk, no obligation and no credit card required free trial. If you fail to be amazed by the amazing plan, no problem, you'll be reverted back to the free tier by the end of the 30 day period.
Do I get a 30-day free trial if I upgrade?
If you upgrade from one tier to another, you are not eligible for the 30-day free trial. The 30-day trial on plans only applies when you sign up for a plan for the first time. You can always downgrade later if you choose.
Do I have to sign an annual contract?
No. You can opt for monthly subscription to be paid monthly. However, the costs of such an arrangement would be higher than the annual subscription. However, if a retailer on monthly subscription does not opt to use the service in future, he would not be charged for future, but any part refund of subscription free already paid will not be given.