To mark an applicant as Reviewed and out of the Needs Review hiring stage, simply select Complete Review Step under the Applicant's name.
Clicking this won't invite them to complete the Assessment step, it will only mark them as Reviewed. You must invite the applicant to the assessment if you wish to move forward with them. (More info: How do I send applicants assessments?)
When you are ready to move forward with the applicant, you can click Invite on a hiring stage. If you know you don't want to move forward with an applicant, click the Make Inactive button to have the option to send them a rejection letter: How do I send a rejection letter to an applicant?