take changes in file sshd_config file without server reboot

Simply restart the sshd service:

sudo service sshd restart

or:

sudo /etc/init.d/sshd restart

There's an even less intrusive way to do this, without restarting the SSH service.

From man sshd:

sshd rereads its configuration file when it receives a hangup signal, SIGHUP, by executing itself with the name and options it was started with, e.g. /usr/sbin/sshd.

So you can use a command like the following to send SIGHUP to the SSH server process:

sudo kill -SIGHUP $(pgrep -f "sshd -D")

The pgrep -f "sshd -D" part will return only the PID of the sshd daemon process that listens for new connections, since there are likely to be other PIDs for each active session that don't need the signal.

For Systemd Systems - Ubuntu default

sudo systemctl reload sshd.service

or

 sudo systemctl reload sshd

or

 sudo /bin/systemctl reload sshd.service

For Sysvinit / Systemd

sudo service sshd reload

or

sudo /etc/init.d/sshd reload

Ubuntu uses systemd: Here the service command passes the units: start, stop, status, and reload through to their systemctl/initctl equivalents.