Button Change image

Hello,

I was wondering how to change the Button image ? am currently using it via php not shortcode, please advise. and also i’m not on a directory like xxx.com/xx/xx/website and when i press login its taking me to xxx.com/steamlogin instead of xxx.com/xx/xx/login any advise ?

Best regards

The page I need help with: [log in to see the link]