Apparently the new logo is uploaded, but not always it is displayed, as other images in the admin panel. This is the error I get:
"GET /img/xprestashop-logo-1507645479.jpg.pagespeed.ic.eEUDLGwQ5j.jpg HTTP/1.1" 403 272
Putting ModPagespeed in off mode in /opt/bitnami/apache2/conf/pagespeed.conf, the problem is solved, but it seems to be a workaround. Is there any other solution to fix this problem, without disabling the "pagespeed module"?