When you're ready to upgrade just click on the "Upgrade" button next to your company account and then select the plan that fits you best. 

However, if you need to access your invoices & payment history, please go to the Company settings, see below. 

The billing settings are a place to find out more about your current plan, expiration date, payment methods, change the credit card you're currently using, see or download your past invoices.

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