Can you send me a link to the profile with such a big avatar? How comes that an image with resolution of 45x45 can be 10Mb? Do you have any examples?

no
Im talking about avatar sources, users can upload big photos then they crops to small avatar 45x45, but original big photos are present in server.

i think that is determined by both the file upload limit set by php and the file size limit set in admin > settings

no :(

look at option 1 if you have access to the php.ini file and option 2 if you do not

http://www.cyberciti.biz/faq/linux-unix-apache-increase-php-upload-limit/

you can always lower the size in the settings also

thanks, but it will affect all uploads.
I think , I'll delete these files manually time by time.