The ability to upload a banner image was not available until version 3.4.0 of links manager. and was for version 1.3.8 of Zen Cart

Links Manager 3.3.0 was the last version available for version 13.7 of Zen Cart.

If you are still using version 1.3.7 of Zen Cart then you should continue using version 3.3.0 of links Manager.