If you're an Admin for your Organisation, you can upgrade to a paid account anytime after your free trial has ended.
To upgrade to a paid account you need to choose a plan:
You will then be required to enter your credit card details after you have confirmed your plan change. If your payment amount is $5,000 or over you will have the payment method option to make manual payments i.e. direct deposit, instead of paying via credit card.
If you're not an Admin for your Organisation, get in touch with someone in your team who is so they can upgrade your Organisation to a paid account.