As a Moderator you can make another participant a Presenter without promoting them to a Moderator. In case of student presentations, the lecturer can make a student Presenter.  

In the meeting click on  the icon in the upper left corner User List Toggle. This opens a vertical bar with the list of meeting participants.

Now, in the participants list:

1. Click on the participant you want to make Presenter in the meeting.
2. Then, from the drop-down menu click on Make Presenter.

Now, with the role of a Presenter the participant has the ability to upload a presentation or share her/his screen, as well as make use of the Annotation tools.

As a lecturer you join the meeting by default as a Moderator and your students as a Viewer. If you want to promote a student to Moderator you can do so.

1. Open user list
2. Click on the participant
3. Select Promote to moderator

In the same way you can demote a participant from Moderator to Viewer if needed.

The participant you promote to Moderator will then have the same options as you, meaning s/he can make someone else a Presenter, can Remove user(s) and Demote other user(s) to viewer.