I want to delete a layout slide in the master file but the "delete" is not an options. Any ideas?

Could be that some slides are using that master layout. In that case, I dont' think you can delete it.

To find out what slides are using what masters, use the pull-out view on the left in slide master view. when you click on a master, it should tell you what slides are being used by that master.

Then for those slides, apply a different layout, then see if you can delete it.