To downgrade your plan, just select Switch To Free Plan. Your subscription will be downgraded at the beginning of the next billing term. You will lose access to all add-ons on when you downgrade. 

When downgrading your plan, your latest applications will be deactivated and your users will be suspended if you have more than allowed by the newly selected plan. You're able to manage applications and users yourself before your plan is downgraded at the end of the billing period. 

If you downgrade to a free plan, your add-ons will be deactivated and you will lose any data and settings that have been set up in the add-ons. However if you downgrade to another paid plan, your add-ons will remain active and would need to be individually deactivated if required.