How can I change to the Spanish language?
At https://docs.civicrm.org/sysadmin/en/latest/install/drupal7/#i18n it links to some instructions at https://wiki.civicrm.org/confluence/display/CRMDOC/i18n+Administrator%27s+Guide%3A+Using+CiviCRM+in+your+own+language

The download link it mentions is a little bit hidden. When you go to https://civicrm.org/download and click on the big download button it's the last one that shows in the dropdown list.