Here are the steps:
1. First sign up on https://app.nanonets.com
2. Pick the model you want to upgrade. For example, if you want to extract data from invoices choose the Invoices model.
3. Then go to "My Models" on the left, this model will show up.
4. Click on "Manage" under the Plan column and add your credit card on the next screen to upgrade to the Pro plan