Windows Server 2012 RDS Devices CAL license

Hi, i want to install RDS CAL license into Server 2012 and mistakenly i have bought RDS devices CAL license. but actually i need it User CAL License so is it possible to change devices CAL license into User CAL License.

if yes what i have to do? to whom i have to contact, other than the partner from whom i have bought.

Thanks in advance.

Regards,

Santo Antony