In short, contact our Support Team!
Our support team can upgrade your plan at no extra cost to you - we do it by changing your plan to the one you need, and shortening your current subscription period according to the difference in price between the plans.
For example: if you have just paid for a year of Professional, you can upgrade to the Business plan without paying extra, but your subscription period would be shortened to 6 months (Business costs twice as much as Professional).
Does this sound good to you? Please message the support team, including the following details, and we'll be happy to upgrade your subscription:
your email for GoLogin
the subscription plan you wish to upgrade to