If paying by check, you will need to sign up for an account, provide the details for your account, then select the Enterprise edition, and click on Register. You will be directed to the purchase details screen where you will select to pay by check. Click on 'Generate Invoice' to print an invoice, confirm the number of license and click ok. You can now print the invoice for your records. You can start using the Standard edition by confirming your email in the email that was sent. Once payment is received we will update your account to the Enterprise edition. Your data will not be lost; it will still be there once you are upgraded to the Enterprise edition.
If you have already created an account and would like to upgrade, see the FAQ while logged into the application on upgrading from the Standard to the Enterprise edition.