Parse Error but can't access dashboard

Using ftp or your host’s file manager software, rename the directory at:
wp-content/themes/square
to
wp-content/themes/old-square

WordPress will be unable to find your theme and will adopt the default theme, enabling you to get back into admin.

Next you will need to debug custom-header.php. You can use this service:
http://phpcodechecker.com/
to validate your code before trying your theme again.

If you have trouble correcting the error in custom-header.php, post the code here:
http://pastebin.com/
and post the pastebin link in this forum. Someone may be able to advise you on line 24.