To change your Wi-fi password, you just need to follow the below steps.
To start, you will need to connect an ethernet cable from your modem directly into your computer.
1. Open an Internet page (Explorer, Firefox etc.) on the computer and in the web address bar type: 192.168.1.1
2. This will ask you to login, type in admin for Username/Password
3. Click on Setup at the top, then Wireless Setup on the left side
4. Select Wireless Connection Setup Wizard
5. Tick the 'Use WPA encryption instead...' then Next
6. Enter the same 8 character long password into the 2.4G/5G band boxes then press Next and then Save
7. Reboot your modem (turn it off at the power point for 10 minutes and then turn it back on again) and your new password will be active.