ACP > Themes > Your theme > Edit > and add a complete path of your new logo in "Board Logo" option field.
Go to Admin CP > Templates & Style > Themes > Your Theme.
Enter the path to the logo or full URL you want in "Board Logo".
i dont have a your theme tab
Yeah, there isn't one.
"Your Theme" means you're supposed to select your theme, in this case it should be "Default".
Then search for "Board URL" and input your image path.