How to upgrade ojs 1 to ojs 3

hi all,
please help me to upgrade ojs version 1 to 3.

we have ojs 1 with 1000 articles and we want upgrade to 3.

i install ojs 3 but when export users xml file from old ojs give this error "
Element ‘users’: No matching global declaration available for the validation root."
becuase xml format in ojs 1 is differnt with ojs 3.

please help me. how to move my data from old ojs (version 1) to new ojs (version 3)