Under Settings > Advanced > Workflow, you can turn on the Require all approvals when manual appointing on or off for your company by checking or unchecking the box: 

This option only applies to cases where one or more approvers have been manually appointed for a document (and not appointed by workflows): 

...then a document can be approved by just one coworker, even if several coworkers have been manually appointed to approve the document. 

For example, if three coworkers have been manually appointed to approve a document, approval will be complete as soon as the first of the three coworkers approves it.

...then the document approval will only be complete after it has been approved by all of the coworkers who have been manually appointed. 

For example, if three coworkers have been manually appointed to approve a document, approval will be complete only after all three have approved it.