This script will set it to 70 million bytes, adjust to taste - not that the number of bytes MUST be as written, not 70M:
---- Cut here ------
#!/bin/sh
/sbin/e-smith/config setprop php PostMaxSize 70000000
/sbin/e-smith/config setprop php UploadMaxFilesize 70000000
/etc/e-smith/events/actions/conf-php
/etc/rc.d/init.d/httpd-e-smith graceful
---- Cut here ------
BTW, this also raises the limit for Horde attachments, if anyone is looking to do that.