(Brother HL-2170W) Change wireless password

To set the wireless password, browse to the printer's ip address which can be found in the router firmware

If the wireless password changed before changing the password at the printer, connect a cat5 cable.
This will use a different ip address, so it's necessary to browse to the wired ip address from the browser

Click on "configure wireless" or something similar
If the SSID changed, click the "browse" button
    This page takes a long time to load as it looks for nearby SSIDs
    The printer can't access the 5 GHz network, so it has to use the 2.4GHz

The wireless configuration asks for keys AND passphrase. Ignore the keys (key1-key4) and just enter the passphrase.
Set the password and save.