VSZ managed APs do not have a web browser UI by default. This firmware is only managed by vSZ controllers. If you no longer have access to the controller the best thing to do would be to factory-reset the APs and load an alternate firmware image such as Unleashed or Standalone, and Unleashed is a good choice for these APs.
After a factory reset, assuming the controller doesn’t adopt your APs again, the web interface will work to let you load on a different image.