I forgot where I can change the site logo, I though it was in the advance configuration under setting but now is gone, help!

ACP - Customization - Appearance - Themes

Pick your theme and click Edit. There will be a tab for logos. 

no you do not understand, the site logo display on the web page

That is not a logo.  It's a favicon.  

ACP - Customization - Appearance - Icons and Logos