Before you do this, check the current wireless network settings including Network Name and Network Key. Now, follow the below mentioned steps:

Connect the Brother printer to the power supply switch
Press Menu and then Up or Down key to choose the Network and then hit OK
Using the same Up and Down keys, select the WLAN and then press OK
Now choose the Setup Wizard using the same keys and press OK
The machine will start searching for your network and you will see a list of SSIDs
Choose the SSID you want to connect and then press OK
Now, do one of the following:
Enter the Network key (if you are using an authentication and encryption method that needs a network key) and then provide the WEP key and press OK. Apply the Settings by clicking Yes
If you have selected an open system method with no encryption mode, then go to the step 8
If the WLAN access router or point you are using supports WPS, then it will be automatically appeared. To connect it to your machine, press WPS button and then press UP arrow key twice
Brother printer will connect to the wireless device you have chosen
You can also see the status "Connected" on the LCD display of the printer
Please Note that the procedure for connecting your Brother printer to a wireless network are more or less. If you find any trouble in accomplishing this process, contact Brother Printer support number.