This article will walk you through how to "recycle" and set up your portal for a new class
2. Consider removing the content created by prior students if not needed by the next class.
Note that when you remove a user, the content they created in the portal remains. If you would like to delete this content, there isn't a bulk way to delete items, so the best way would be to click the box at the top right corner of the asset/tool to "check" everything and then delete. Here's some guidance on deleting CRM records as an example.
3. Add new students by creating the proper Student Permission Set and inviting students to the portal.