Yes it can get better artwork from Discogs
If you have a value in the Discogs Release Url field. If you do you can run ‘Update tags from Discogs’ and this will update various fields from the Discogs database including the artwork, and Discogs artwork is usually quite high resolution. But you have to modify ‘Preferences/Remote Correct/Discogs/Artwork’ to ‘Populate this field if empty’ because by default it is set to ‘Never Populate this field’ (because if you are using iTunes this will override the artwork downloaded by iTunes but not stored in the file itself - only stored in the iTunes database.
How do you get a Discogs Release Url ? If the track is corrected by Musicbrainz it may have added one in, or you can go to the Discogs website yourself and manually search for one yourself and add it in. In later versions of Jaikoz there will also be an AutoCorrect Tags from Discogs that will try to find the release id automatically
To delete all the artwork just select the artwork fields , bring up popup menu (or use Main Menu/Edit menu) and select Delete.