One of the nice things that changed recently in CRM Online is the ability to change the instance type of a CRM organization. That means you can change from a production org to a sandbox. This feature is also enabled for the CRM Online trials, so while you are trying CRM out you can make the most of your trial by using features like reset. So for example if you try a few thigns out, realize you want to do it differently, you can simply reset your CRM organization back to how it started. You can also reset to older versions of CRM. Currently, you are able to go to CRM 2016, CRM 2015 Update 1, CRM 2015 and CRM Spring Update 2014. So how do you do this?
From portal.office.com navigate to Admin -> CRM and you will see the CRM Online Administration Console - on the console - click Edit
From there you will see the edit instance dialog, modify the instance type to be Sandbox.
After you click next you will see a confirmation page. This is a good time to make sure you are not converting your "real" production :)
Now when you get back to the list of CRM organizations you will now see a set of new controls that include Reset next to the instance.