How do I delete from ipad after having deleted from itunes on computer

You can delete music directly on the iPad, either directly in the Music app by swiping/dragging from right-to-left on the track, album or artist selection screens (depending upon whether you want to delete individual tracks, whole albums, or all of an artist's tracks) - or you can do similar in Settings > General > Usage > Manage Storage > Music

Or you can connect your iPad to your computer, select its icon in your computer's iTunes, and then select the Music heading under the 'On My Device' section and use that screen to select and delete your music from it