Step 1: Open web browser and type LAN IP address of the ADSL router in the address bar and press Enter. The default IP address of TP-LINK ADSL router is 192.168.1.1.
Step 2: Type the username and password in the login page. The default username and password are both admin in lowercase.
Step 3: Click Management->Access Control->Password on left page select your login username and type the old password and new password.
Step 4: Click Save/Apply to save the settings.
You need to access your router's setup page (usually https://192.168.1.1, https://192.168.0.1 or https://10.1.1.1).
It will ask you for a username/pass. By default this is usually admin/[blank] or admin/admin check with your router's manual for clarification.
There should be a page with wireless settings you'll want to use WPA or WPA2 encryption (as WEP is worthless easily crackable) with a password consisting of uppercase and lowercase letters numbers and symbols (e.g. agRa$29bXA) the longer the better.
How To Setup TP Link Router Password?