Switch your plan in case you need to adapt your constant content output. You can switch it at any time and as often as you prefer. Just go to Account Settings > Plans and directly switch the plan.
Upgrading your plan
In case you upgrade a plan you can instantly take more photos and a new billing cycle starts. If you still had remaining photos left don't worry, these will be saved for later use and do not expire. If your old plan has exceeded the monthly limit, you don't have to pay for that too. However, your new plan will start with the number exceeded.
Example: You subscribed to the Starter Plan and took 15 photos exceeding the monthly limit by 5. Now you'd have to pay an additional fee. By upgrading, this fee doesn't apply, but you'll start with 5 photos in your new plan.
Downgrading your plan
When downgrading, you keep the current plan until the period is over and then automatically switch to the new plan. This holds true for the current and all following periods until you decide to cancel. Credits will adapt to the new plan as soon as the next billing period starts.
In case of downgrading your zerolens subscription, the new plan will take effect when the old one ends. This happens automatically.