Hi Alessandro,
the location is set at the bottom in the Main settings.
I still dont understand why you want to use the whos-online plugin. Google Analytics will give you much more options - it will show you number of visitors, which country they came from, how long they spent on your site, which sites are being visited etc.
It is also built-in the template, so it will count visits to all pages of the template, not just homepage and in google analytics you can then view graphs, tables, choose time intervals etc etc. Even real-time values. So Im not sure I get why you want to try implementing a different script, which Im not sure will work because it is likely to clash with other scripts and it will do nothing more than GA can do.