Yes you can.
However, be advised that if you activate a different type of a plan compared to your currently active plan, you’ll lose the currently active plan and the new plan will start immediately.
More detailed instructions about this is available on the activation page on Ruuvi Station web interface. For more info, see the other FAQ topics and also the activation help page in the header menu of this page.
In the future, we are aiming to make it possible to migrate a smaller plan to a bigger one without completely losing unused time of the smaller plan. Please note that this feature is not implemented yet. If you need to switch to a bigger plan before the feature is available, contact us by email.