Our license terms allow for developers for create sites for clients using our themes, however this does not automatically make their client an AppThemes customer (with access to theme updates and support). If however he has purchased the theme for you, with the account in your name we can check further. Please
email us with any information you have regarding the original purchase (i.e. transaction ID, full name on the account, email address which may have been used at the time).
Otherwise yes you would need to purchase your own theme license in order to access updates and support. Pricing can be found
here, and whether or not you'll be effected by upgrading to the latest version will depend on whether or not you have any modifications made to the original theme. Thanks.