Click on the "Tweak Settings" link under "Server Setup". Within the "Stats and Logs" section is a text box with the heading:
"Chmod value for rawApachee log files (0640 is the default):"
Change the value to suit your needs and apply the changes by clicking on the "Save" button at the bottom of the page.
Most programs only need read permissions on the log files so setting this to 0644 should suffice.