If the "Update" sticker appears, then the software detected that the files on the server are newer than on your computer. Of course this is only possible if these shows have been downloaded before.

It is possible that some files have been exchanged because of problems. This usually happens after a user has reported issues with a particular clip on a show.

All the files in a show have been changed (upgrade), if the shows are now in a higher resolution. This usually also the colors are slightly improved.