You can change the number of users or your subscription plan anytime you want. Ragic pro-rates subscription changes, and this is how prorating is handled if you change details of your subscription:
(ex. monthly payment to yearly payment)
The first full period of the billing cycle begins immediately, and you will be charged for the first period less the account balance.
For example,if a customer signs up on May 1 for a plan that costs $30 per month and then switches to a yearly plan that costs $300 on May 15. The customer is credited $15 for the unused portion of the monthly plan and owes $300 for the first year of the new plan. The customer is invoiced—at the time of the switch—$285, and the annual billing cycle begins that day.
(Note that if the payment fails, the plan change will not go into effect).
The first full period of the new plan begins immediately. However, you'll be charged for the first period less the account balance in upcoming billing date.
Besides, a downgrade will generate a credit to be applied to the next invoice. If your account balance amount is larger than the amount due (if you have decreased the number of users), you won't be charged anything, and the account balance is carried over to future billing periods, until it's spent down.
For example, if a customer signs up on May 1 for a $10 plan, she'll be billed $10 immediately. If she then switches to a $20 plan on May 15, on June 1 she'll be billed $25 ($20 for a renewal of her subscription and a $5 prorating adjustment for the previous month).
Here is an example of changing the subscription plan and number of users for your reference
Learn how to modify your subscription here.