How to make log-rotate change take effect

logrotate uses crontab to work. It's scheduled work, not a daemon, so no need to reload its configuration.
When the crontab executes logrotate, it will use your new config file automatically.
If you need to test your config you can also execute logrotate on your own with the command:

logrotate /etc/logrotate.d/your-logrotate-config

Or as mentioned in comments, identify the logrotate line in the output of the command crontab -l and execute the command line refer to slm's answer to have a precise cron.daily explanation

Most of the logrotate setups I've seen on various distros runs out of the /etc/cron.daily. There's a shell script there aptly named logrotate.

Example

$ ls -l /etc/cron.daily/logrotate 
-rwxr-xr-x 1 root root 180 May 18  2011 /etc/cron.daily/logrotate

Manual run

If you want to make it run manually simply run the script as root:

$ sudo /etc/cron.daily/logrotate

If you take a look at a script that's typically there, it shows you how you can also run logrotate manually, by simply running logrotate + the path to its configuration file.

#!/bin/sh

/usr/sbin/logrotate /etc/logrotate.conf
EXITVALUE=$?
if [ $EXITVALUE != 0 ]; then
    /usr/bin/logger -t logrotate "ALERT exited abnormally with [$EXITVALUE]"
fi
exit 0

It should be automatic via cron. You can force it to test your changes.

For global logrotate:

sudo logrotate -v -f /etc/logrotate.conf

For a single conf file:

sudo logrotate -v -f /etc/logrotate.d/someapp.conf