At anytime you can go in to your billing settings and change your subscription tier.
Step-by-Step Instructions to change your subscription tier:
Go to Billing Portal
In the Web Version of Heidi Navigate to the billing portal using the Account tab:
Once there, you can "Manage my billing" from your Heidi account settings
View Subscription Options
On the subscription overview page (Image 1), click "Update subscription".
Select Your preferred plan
In the update screen (Image 2):
Find the plan you are looking for.
Click Select under the plan you wish to change to.
Confirm Update
Review the pricing and click Continue to proceed.
Follow prompts to finalise the change.
Verify Change
Return to the Account page.
Check that it now shows the correct plan.