All your devices must be updated and compatible to work smoothly. Usually you receive a notification about an update otherwise keep a check through website.
Here’s the steps for Arris TG862 firmware update. Steps for update:
Select status from set up page on the router interface.
There will be a drop down menu. Chose router upgrade.
Download the file and save it.
Go to the downloaded file.
Now, select upgrade and confirm it.
The file will be uploaded and installed automatically.
Read more: hard reset arris router