hi Torsten! For future reference, this is always available for you in the Aerohive Deployment Guide, which can be found by going to HiveManager - Help (in the upper right) and clicking on "Videos and Guides".
For immediate reference - Aerohive devices connect to HiveManager one of two ways: either using UDP 12222 (CAPWAP) and SSH (to download complete configs and firmware updates), or via HTTP and HTTPS. You can force CAPWAP over HTTP if you wish, and if you have a proxy server at your school you can even set it to use a proxy configuration. Let us know if this works!