Please make sure that permissions for the following files and folders are set to 777 (drwxrwxrwx for the folders and -rwxrwxrwx for the files):

admin/data/users.xml
admin/logs/
admin/xml/
admin/xml/all content
admin/config.xml
fonts/
images/
media/
music/
xml/
xml/all content
config.xml
admin/_tmp/all content
admin/actions/backup/_backups/

Also, following files should have permissions set to 755 (-rwxr-xr-x):
/admin/actions/upload_media.php
/admin/actions/upload_fonts.php
/admin/gateway.php

The rest of the files should have the permissions set to 644. The rest of the folders should have the permissions set to 755.

You can watch video tutorial following this link