You can change your plan whenever you would like, Downgrade, Upgrade or just change the billing cycle it makes no difference. To change your plan go to the Manage Account page under the Billing section.
Then you will just need to click on Edit for your current hosting plan.
You will then be able to choose with plan you would like to change to or which new billing cycle you would like to setup.
Note: If you change your plan your plan will restart from that day and you will receive an early ending credit for the unused time of your original plan which will be applied to your new plan.
Then you just need to click on
and then pay for the difference in the plans if there is any
And you're done.