I'm not sure whether you want to add or delete the logo, however, the best place to add it/ look for it to delete, will be the master slide. This isn't one of the slides you display but contains all the 'standard data' that appears on every slide.
Go to View in your toolbar and select Master, Slide Master and make any edits you want and then save the presentation.
The other possibility is that the logo has been 'grouped' with other data on the slide and can't be deleted on its own. In this case select the logo (and all the other data) and go to Draw and select Ungroup. It may be necessary to repeat this step depending on how deeply the logo is nested in the data. When the logo can be selected on its own, then you can delete it.