I’m not too familiar with this device but looking online it appears to be quite a specialist thing designed for home security so not sure if you would be able to put a custom ROM on like other Android tablets - the process might be tricky or simply not been tried out by the hacking community that find ways to ‘root’ and update these devices
However if you are just looking for how to update it it appears AT&T who make the device offer this video guide that might help you: