I'm here to sort things out with you, situ.

The Run report drop-down is in the Classes list page. Also, we can't totally delete a Class however, we can inactivate them which also reduces the number of usage. I'll provide the steps again and have attached some screenshots for your reference. 

1. At the upper-right, click the Gear icon and select All Lists. 
2. Click on Classes. 
3. Let's look for the class to inactivate. 
4. Under the ACTION column, click the drop-down arrow beside Run report. 
5. Click Make inactive. 
6. Select Yes to confirm. 

If we want to see a list of all our classes including the inactive ones, still in the Classes page, click the small gear icon above the ACTION column. 

We can also run reports that have classes with in it. You can refer to this article for more details on how to add classes on a report.

Feel free to get back to me if you need anything else. Take care!