In order to manually update the firmware on your MiniNova using a Mac:
1) Please download SysEx Librarian from here
2) Please download the attached 1157.syx file for the MiniNova, this is the OS update.
3) Open SysEx Librarian.
4) click 'Add…' and then select the MiniNova 1157.syx fie you downloaded.
5) Connect the MiniNova to your Mac via USB and power up the MiniNova via USB while pressing 'PAGE <', 'PAGE >' and 'OK'. You should see 'Exit to firmware' shown on the LCD screen.
6) Select the MiniNova as the destination in SysEx Librarian.
7) Select the 1157.syx file and then press the play button in SysEx Librarian.
8) SysEx Librarian should now show that it's sending the update and the MiniNova should also show this on it's LCD screen.
9) Once complete the MiniNova will re-boot and you can confirm which firmware is installed in the Global menu of the unit.
If you have any further problems, contact Novation Technical Support here.