Have a look a this page: http://docs.moodle.org/en/Installing_Moodle
Especially:
You can also do things like define the maximum size for uploaded files:
LimitRequestBody 0 php_value upload_max_filesize 2M php_value post_max_size 2M
You can also do things like define the maximum size for uploaded files:
LimitRequestBody 0 php_value upload_max_filesize 2M php_value post_max_size 2M