If you have canceled your subscription at the end of the period, you might run into this issue. You can follow the below steps to upgrade your plan.
1. Go to your profile in the top right corner, and select 'Manage Payments' on the dropdown menu.
2. This will open a new tab that takes you to your Stripe payment portal. Click 'Renew plan'. This will only resume the future plan you canceled, and will not cause any charge now.
3. Once you renew the plan, you should see an option to upgrade your plan.
4. Click 'Update plan', you can choose which plan you would like to upgrade to.
If you have any questions regarding your account and subscription, check out our guides.