I have personally found that to upgrade such an old wiki can be a headache. You could try by first backing everything up. See:
https://www.dokuwiki.org/install:upgrade,
If that fails, this wiki doesn't seem to have a huge amount of data, so the least error prone way to upgrade might be to start a new install and to load into it your data/pages, data/media files. Then if you have more than one user, you can take what you need from and conf/acl.auth.php and conf/users.auth.php.