Did you try editing concrete5 Login>Dashboard>Scrapbook>Global>My_Site_Name?
There are multiple places in which it can be found.
one is as Pauls mentioned.
another one is in the Theme you use and then the header.php (found in your FTP /themes/themename/elements or /concrete/themes/themename/elements), it might say "MY SITE" in there.
You can also find code in de header.php which might look something like this in there:
if you have this code in there then you can change it like this: under dashboard -> sitewide settings, change the sitename (ofcourse you can also try this without checking the header.php file)
one is as Pauls mentioned.
another one is in the Theme you use and then the header.php (found in your FTP /themes/themename/elements or /concrete/themes/themename/elements), it might say "MY SITE" in there.
You can also find code in de header.php which might look something like this in there:
if you have this code in there then you can change it like this: under dashboard -> sitewide settings, change the sitename (ofcourse you can also try this without checking the header.php file)