You can upgrade from any level to any level at any time by clicking on the Upgrade or Downgrade link below the desired plan you want to switch to and confirm the dialog that pops up.
Upgrades and downgrades take effect immediately. The new monthly rate begins at the start of your next billing cycle.
Go to Accounts > Overview
On the Overview page scroll down to Upgrade / Downgrade Plan
Account Overview page
Why can’t I downgrade?
In order to preserve your assets, you can only downgrade to a level that can handle your current amount of assets, users and stages.
For example, if you currently use 1000 MB of storage space in you Fluxiom account you can’t downgrade to the Basic plan because the Basic plan only allows 800 MB storage space. You’ll have to delete files first before you can downgrade to the Basic plan.