Deleting/Removing members from your Workspace doesn't automatically lead to the downgrade of your plan.
In other words, you need to do both actions (Deleting members + Downgrading your subscription).
Here is how to downgrade your subscription :
1. Remove member(s) - also called (user(s)) - from your Workspace (see our article here)
2. Once you have removed user(s), kindly click the 'Plans & Billing' tab and click 'Downgrade
Please let us know if you have any questions or if you need further assistance.