To delete artwork from multiple songs:
1. Highlight all of the songs.
2. Right-click and left-click Get Info.
3. At the top where you have the box for the artwork, click on it and it should become highlighted with a blue border.
4. Once highlighted, press delete on the keyboard. Whatever image is shown will now turn into a grey box.
5. Click OK and the artwork will be removed from the selected songs.
To paste any image from the Get Info window:
1. Click on the Artwork menu.
2. On the top left, click the box next to the Album Title/Song Title. Once selected it will be highlighted with a blue border.
3. Ctrl+V will paste the image and you'll see the larger image below the highlighted box.
4. Click OK to save.
Alternatively:
You can skip step 2 and just hit Ctrl+V while in the Artwork pane. Click OK to Save. Saves some time. 🙂
Hope this helps!