1) Please use the same version of firmware on the new Controller as old one and 2) restore the backup of old controller and restore the configuration A) select the first option to restore everything and 3) remove the old one and 4) connect new controller
I assume that you don't have admin credentials for the old controller (if you do, just login, pull your own backup, and follow Abi's post). If you don't have admin credentials, and you don't care about issued guest passes, DPSK, and mesh, and provided that you know enough about the current config (WLANs, ACLs, VLANs, etc), you could config the new controller from scratch. Assign the same address, swap the boxes, and reboot the APs. Firmware on the new controller does not necessarily need to be the same as the old one as long as it's a version that supports the 7982.