Good Day forerscrm,
If I understand you correctly; you want to change your Wifi-Router password itself (Normally defaulted to admin etc.)
First step is to get your gateway address, this is done by:
Step One A
Check under your Router and see if you can find something called "Gateway" on the label should be in this format (192.168.8.1/10.0.0.2 etc.)
If found, write it down. Else proceed below to Step One B
Step One B
pressing CTRL + R on your windows computer, a window will open on the bottom left part of the screen called "Run" in the textbox of that window, type 'cmd' (without the ' ') a black window will now open called Command Prompt or cmd.exe
In the black command window type 'ipconfig'
You should now see all your network adapters appear find the one that you connect to (WIFI or Ethernet)
Under the Adapter name will be a line called Default Gateway, write down that ip address should be in this format (192.168.8.1/10.0.0.2 etc.)
You have now completed Step 1 :)
Open your web browser
In the URL field type your Gateway adress that you previously wrote down ( 192.168.8.1 / 10.0.0.2 etc.) and navigate to it.
If you reached your router you will be prompt for login or you might be auto-logged in in the event that it does not have a password.
For the password, check under the router (Default might be: admin)
When you logged in successfully, you have reached the second tricky part, finding the right tab. It will be under something called "system" or "security" or "device" etc. probably near the bottom of the navigation bar.
Once you found it, you may enter your Old password and New password and press confirm/accept to change it.
You are now done !
In the event that you might have forgotten your Router password, you will need to reset the router to it's factory defaults. BEFORE you attempt this, make sure you have the ISP POPPE details with you as you will have to setup the entire router from scratch. Continuing, locate that reset pin hole (or there could be a reset button, refer to the router manual) and hold it in till the router's power light is the only light lit (it might differ with some devices, but you will notice once it resets) then release the button.
Log into your router and it will be freshly 'formated' and you can start setting it up again :)