How to stop Wifi leakage

[Anooprs09]

Hi
I am using D-Link N150 wifi router and it has been using by somebody. How do i stop this could you please help me on this

 

[kanewolf]

• 
  ■ Change the password IMMEDIATELY
  ■ Use WPA2 encryption.
  ■ Use a strong password -- At least 12 characters, At least 2 Upper, 2 numbers and 2 special characters. Use a random password generator website if needed.
  ■ Change your password regularly (90 to 180 days)
  ■ Disable WPS on the router.