When I have wrong artwork I fix it one of two ways:
Browse to: '%AppData%\J River\Media Center 22\Cover Art'
In the Series folder, put the correct artwork with the filename SeriesName.ext - example would be 'Better Call Saul.jpg'
In the Seasons folder, put the correct artwork with the filename SeriesName - Season XX.ext - example would be 'Better Call Saul - Season 2.jpg'
In the main UI, I have a view called Shows (Covers) that is a 'View As' Categories and has the categories of Series and Season. This gives me a list of all of my series with their cover art and when I open one I get the seasons with cover art and individual episodes. I then just right click on the appropriate item and use the 'get from internet' feature or add from file, or paste as appropriate.