Go to Settings → Billing
Click Manage Subscription to open the Stripe Customer Portal
Select your new plan
Upgrading
When you upgrade, the new plan takes effect immediately. You'll be charged the prorated difference for the remainder of your current billing cycle.
Downgrading
When you downgrade, the change takes effect at the end of your current billing cycle. If your current usage exceeds the lower plan's limits (products or team members), you'll need to reduce usage before the downgrade can complete.