I upgraded firmware, but the WIFI modem can't be connected to AP after I set the module the same as with old firmware.

Use AT&F to reset everything back to factory default.

Use AT#RESET to reboot / restart the module.

Use these basic commands to connect to AP:

at#wlanssid=ssid-name
at#wlanenable=1
at#ipdhcp=1
at#uartflowcontrol=1