There are a couple of ways to approach this depending on just how many emails you are talking about. If you mean just a few, check the little box to the left of each one in the message list, then click on the trashcan icon in the toolbar. If you want to get rid of a bunch of them, and they are in continuous sequence, check the box for the first one, then holding down the Shift key, scroll down to the last one in the group and check that one. That will select everything in between. Then again hit the trashcan icon.